Fix an incorrect autocorrect for Style/IfWithSemicolon

[koic]

This PR fixes an incorrect autocorrect for Style/IfWithSemicolon when the then body contains an arithmetic operator method call.

Before

Autocorrect makes invalid syntax:

$ echo 'if cond;do_something - arg end' | bundle exec rubocop --stdin dummy.rb -a --only Style/IfWithSemicolon
Inspecting 1 file
F

Offenses:

dummy.rb:1:1: C: [Corrected] Style/IfWithSemicolon: Do not use if cond; - use a ternary operator instead.
if cond;do_something - arg end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
dummy.rb:1:21: F: Lint/Syntax: -' interpreted as argument prefix
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter, under AllCops`)
cond ? do_something -(arg) : nil
                    ^
dummy.rb:1:28: F: Lint/Syntax: unexpected token tCOLON
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter, under AllCops)
cond ? do_something -(arg) : nil
                           ^

1 file inspected, 3 offenses detected, 1 offense corrected
====================
cond ? do_something -(arg) : nil

After

Autocorrect makes valid syntax:

$ echo 'if cond;do_something - arg end' | bundle exec rubocop --stdin dummy.rb -a --only Style/IfWithSemicolon
Inspecting 1 file
C

Offenses:

dummy.rb:1:1: C: [Corrected] Style/IfWithSemicolon: Do not use if cond; - use a ternary operator instead.
if cond;do_something - arg end
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected
====================
cond ? do_something - arg : nil

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.