False positive modifier_order violation when explicit order is not specified

[abdulowork]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

False positive modifier_order violation is reported when final keyword precedes public keyword if order between two is not specified explicitly.

As far as I understand the rule it should only validate the ordering between keywords specified by the configuration keyword groups and leave unspecified declarations in place.

Complete output when running SwiftLint, including the stack trace and command used

Here is the config

whitelist_rules:
  - modifier_order

modifier_order:
  preferred_modifier_order:
    # - final #uncommenting this makes the violation go away
    - override
    - acl

Here is the output

echo 'final public class Foo { }' | swiftlint lint --no-cache --use-stdin
Loading configuration from '.swiftlint.yml'
<nopath>:1:14: warning: Modifier Order Violation: public modifier should be before final. (modifier_order)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version (run swiftlint version to be sure)?

0.27.0

• Installation method used (Homebrew, CocoaPods, building from source, etc)?

building from source

• Which Xcode version are you using (check xcode-select -p)?

9.4.1

[jpsim]

Resolved in #2458