Fix an infinite loop error for Style/EmptyMethod

[koic]

This PR fixes the following infinite loop error for Style/EmptyMethod.

% cat example.rb
def foo(arg
    ); end

Before

The following error occurs without auto-correction.

% bundle exec rubocop --only Style/EmptyMethod -a example.rb
(snip)

Offenses:

example.rb:1:1: C: [Corrected] Style/EmptyMethod: Put empty method
definitions on a single line.
def foo(arg ...
^^^^^^^^^^^^

0 files inspected, 1 offense detected, 1 offense corrected
Infinite loop detected in
/Users/koic/src/github.com/koic/rubocop-issues/empty_method/example.rb.
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:288:in `check_for_infinite_loop'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:271:in `block in iterate_until_no_changes'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:270:in `loop'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:270:in `iterate_until_no_changes'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/runner.rb:241:in `do_inspection_loop'
(snip)

% cat example.rb
def foo(arg
    ); end

After

Auto-corrects without any error.

% bundle exec rubocop --only Style/EmptyMethod -a example.rb
(snip)

Offenses:

example.rb:1:1: C: [Corrected] Style/EmptyMethod: Put empty method
definitions on a single line.
def foo(arg ...
^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense corrected

% cat example.rb
def foo(arg); 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.