Fix a false negartive for Performance/RegexpMatch

[koic]

Follow up rubocop/rubocop#6965.

This PR fixes a false negartive for Performance/RegexpMatch when using RuboCop 0.68 or higher.

# example.rb
def foo
  if /re/.match(foo, 1)
    do_something
  end
end

RuboCop 0.67

RuboCop 0.67 warns.

% rubocop _0.67.2_ --only Performance/RegexpMatch
Inspecting 1 file
C

Offenses:

example.rb:2:6: C: Performance/RegexpMatch: Use match? instead of match
when MatchData is not used.
  if /re/.match(foo, 1)
     ^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

RuboCop 0.68 (Before)

RuboCop 0.68 does not warn. This is a false negative.

% rubocop _0.68.1_ --only Performance/RegexpMatch --require
rubocop-performance
Inspecting 1 file
.

1 file inspected, no offenses detected

RuboCop 0.68 (After)

This PR fixes a false negative.

% rubocop --only Performance/RegexpMatch --require rubocop-performance
Inspecting 1 file
C

Offenses:

example.rb:2:6: C: Performance/RegexpMatch: Use match? instead of match
when MatchData is not used.
  if /re/.match(foo, 1)
     ^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

This fix uses the following <> node pattern notation introduced in RuboCop 0.68, so it supports Ruby version 0.68 or higher.
rubocop/rubocop#6965

---

Before submitting the PR make sure the following are checked:

• 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.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

I will release RuboCop Performance 1.2.0 after being merged with this PR.

[bquorning]

I think we should add a spec example that would catch this.

[koic]

My description was lacking. I noticed that existing tests are falling.
https://circleci.com/gh/rubocop-hq/rubocop-performance/419

So I think that there is no need to add a test to this PR because they are covered by existing tests.

I think that it is good to add a test of NodePattern to RuboCop Core if adding a test.