Fixes standardrb/standard#230.

This PR fixes the following incorrect auto-correct for Performance/ReverseEach when using multi-line reverse.each with leading dot.

% cat example.rb
[1, 2, 3]
  .reverse
  .each do |idx|
    puts idx
  end

Before

% bundle exec rubocop -a --only Performance/ReverseEach
% cat example.rb
[1, 2, 3]
  .reverse
  _each do |idx|
    puts idx
  end

After

% bundle exec rubocop -a --only Performance/ReverseEach
% cat example.rb
[1, 2, 3]
  .reverse_each do |idx|
    puts idx
  end

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.