Support the latest rubocop

[akiomik]

I got the following error when I ran bundle exec rake with the latest version of rubocop, so I fixed it in this PR.

warning: parser/current is loading parser/ruby26, which recognizes                                                                                                               
warning: 2.6.6-compliant syntax, but you are running 2.6.0.                             
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.                                                                                            
Running RuboCop...                                                                                                                                                               
.rubocop.yml: Metrics/LineLength has the wrong namespace - should be Layout                                                                                                      
Error: The `Lint/HandleExceptions` cop has been renamed to `Lint/SuppressedException`.  
(obsolete configuration found in .rubocop_todo.yml, please update it)                                                                                                            
The `Naming/UncommunicativeMethodParamName` cop has been renamed to `Naming/MethodParameterName`.                                                                                
(obsolete configuration found in .rubocop_todo.yml, please update it)                                                                                                            
`Performance/*` has been extracted to the `rubocop-performance` gem.                                                                                                             
(obsolete configuration found in .rubocop_todo.yml, please update it)                                                                                                            
RuboCop failed!  

warning: parser/current is loading parser/ruby26, which recognizes
warning: 2.6.6-compliant syntax, but you are running 2.6.0.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
Running RuboCop...
.rubocop.yml: Metrics/LineLength has the wrong namespace - should be Layout
The following cops were added to RuboCop, but are not configured. Please set Enabled to either `true` or `false` in your `.rubocop.yml` file.

Please also note that can also opt-in to new cops by default by adding this to your config:
  AllCops:
    NewCops: enable

Layout/SpaceBeforeBrackets: # (new in 1.7)
  Enabled: true
Lint/AmbiguousAssignment: # (new in 1.7)
  Enabled: true
Lint/DeprecatedConstants: # (new in 1.8)
  Enabled: true
Lint/DuplicateBranch: # (new in 1.3)
  Enabled: true
Lint/DuplicateRegexpCharacterClassElement: # (new in 1.1)
  Enabled: true
Lint/EmptyBlock: # (new in 1.1)
  Enabled: true
Lint/EmptyClass: # (new in 1.3)
  Enabled: true
Lint/LambdaWithoutLiteralBlock: # (new in 1.8)
  Enabled: true
Lint/NoReturnInBeginEndBlocks: # (new in 1.2)
  Enabled: true
Lint/RedundantDirGlobSort: # (new in 1.8)
  Enabled: true
Lint/ToEnumArguments: # (new in 1.1)
  Enabled: true
Lint/UnexpectedBlockArity: # (new in 1.5)
  Enabled: true
Lint/UnmodifiedReduceAccumulator: # (new in 1.1)
  Enabled: true
Style/ArgumentsForwarding: # (new in 1.1)
  Enabled: true
Style/CollectionCompact: # (new in 1.2)
  Enabled: true
Style/DocumentDynamicEvalDefinition: # (new in 1.1)
  Enabled: true
Style/EndlessMethod: # (new in 1.8)
  Enabled: true
Style/HashExcept: # (new in 1.7)
  Enabled: true
Style/NegatedIfElseCondition: # (new in 1.2)
  Enabled: true
Style/NilLambda: # (new in 1.3)
  Enabled: true
Style/RedundantArgument: # (new in 1.4)
  Enabled: true
Style/SwapValues: # (new in 1.1)
  Enabled: true
Performance/AncestorsInclude: # (new in 1.7)
  Enabled: true
Performance/BigDecimalWithNumericArgument: # (new in 1.7)
  Enabled: true
Performance/BlockGivenWithExplicitBlock: # (new in 1.9)
  Enabled: true
Performance/CollectionLiteralInLoop: # (new in 1.8)
  Enabled: true
Performance/ConstantRegexp: # (new in 1.9)
  Enabled: true
Performance/MethodObjectAsBlock: # (new in 1.9)
  Enabled: true
Performance/RedundantSortBlock: # (new in 1.7)
  Enabled: true
Performance/RedundantStringChars: # (new in 1.7)
  Enabled: true
Performance/ReverseFirst: # (new in 1.7)
  Enabled: true
Performance/SortReverse: # (new in 1.7)
  Enabled: true
Performance/Squeeze: # (new in 1.7)
  Enabled: true
Performance/StringInclude: # (new in 1.7)
  Enabled: true
Performance/Sum: # (new in 1.8)
  Enabled: true
For more information: https://docs.rubocop.org/rubocop/versioning.html
Inspecting 21 files
......W..C..C........

Offenses:

lib/rantly/generator.rb:3:5: C: [Correctable] Layout/EmptyLinesAroundAttributeAccessor: Add an empty line after attribute accessor.
    attr_writer :default_size
    ^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rantly/generator.rb:34:5: W: Lint/MissingSuper: Call super to initialize state of the parent class.
    def initialize(limit, nfailed) ...
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rantly/generator.rb:194:3: C: Metrics/CyclomaticComplexity: Cyclomatic complexity for freq is too high. [9/7]
  def freq(*pairs) ...
  ^^^^^^^^^^^^^^^^
lib/rantly/generator.rb:194:3: C: Metrics/PerceivedComplexity: Perceived complexity for freq is too high. [9/8]
  def freq(*pairs) ...
  ^^^^^^^^^^^^^^^^
lib/rantly/property.rb:8:19: C: [Correctable] Style/RedundantFetchBlock: Use fetch('RANTLY_VERBOSE', 1) instead of fetch('RANTLY_VERBOSE') { 1 }.
  VERBOSITY = ENV.fetch('RANTLY_VERBOSE') { 1 }.to_i
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rantly/property.rb:9:22: C: [Correctable] Style/RedundantFetchBlock: Use fetch('RANTLY_COUNT', 100) instead of fetch('RANTLY_COUNT') { 100 }.
  RANTLY_COUNT = ENV.fetch('RANTLY_COUNT') { 100 }.to_i
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/rantly/property.rb:13:15: C: [Correctable] Style/GlobalStdStream: Use $stdout instead of STDOUT.
              STDOUT
              ^^^^^^
lib/rantly/property.rb:44:25: C: [Correctable] Naming/RescuedExceptionsVariableName: Use e instead of boom.
    rescue Exception => boom
                        ^^^^
lib/rantly/shrinks.rb:4:5: C: [Correctable] Style/RedundantAssignment: Redundant assignment before returning detected.
    shrunk = if self > 8 ...
    ^^^^^^^^^^^^^^^^^^^^

21 files inspected, 9 offenses detected, 6 offenses auto-correctable

Tip: Based on detected gems, the following RuboCop extension libraries might be helpful:
  * rubocop-minitest (http://github.com/rubocop-hq/rubocop-minitest)
  * rubocop-rake (http://github.com/rubocop-hq/rubocop-rake)

You can opt out of this message by adding the following to your config (see https://docs.rubocop.org/rubocop/extensions.html#extension-suggestions for more options):
  AllCops:
    SuggestExtensions: false
RuboCop failed!

[diasbruno]

It would be nice to also add to the test matrix recent ruby versions.

[abargnesi]

Hi Akiomi. Thanks for the contribution to updating rubocop. Great idea.