Fix cache with non UTF-8 offense message

[pocke]

Problem

If offense message's encoding is not UTF-8, the cache system raises an error.

Offense message can be an ASCII-8BIT if the offense message is constructed with ASCII-8BIT source code.
For example, YodCondition cop's message will be it.

test.rb

# encoding: ascii-8bit

x = ''

if "あ" == x
end

$ rubocop --only YodaCondition
"\xE3" from ASCII-8BIT to UTF-8
/home/pocke/.rbenv/versions/trunk/lib/ruby/2.7.0/json/common.rb:224:in `encode'
/home/pocke/.rbenv/versions/trunk/lib/ruby/2.7.0/json/common.rb:224:in `generate'
/home/pocke/.rbenv/versions/trunk/lib/ruby/2.7.0/json/common.rb:224:in `generate'
/home/pocke/.rbenv/versions/trunk/lib/ruby/2.7.0/json/common.rb:394:in `dump'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/cached_data.rb:17:in `to_json'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/result_cache.rb:116:in `block in save'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/result_cache.rb:115:in `open'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/result_cache.rb:115:in `save'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:211:in `save_in_cache'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:143:in `file_offense_cache'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:122:in `file_offenses'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:110:in `process_file'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:87:in `block in each_inspected_file'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:86:in `each'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:86:in `reduce'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:86:in `each_inspected_file'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:73:in `inspect_files'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/runner.rb:39:in `run'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/cli.rb:210:in `execute_runner'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/cli.rb:80:in `execute_runners'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/lib/rubocop/cli.rb:51:in `run'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/exe/rubocop:13:in `block in <top (required)>'
/home/pocke/.rbenv/versions/trunk/lib/ruby/2.7.0/benchmark.rb:308:in `realtime'
/home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.7.0/gems/rubocop-0.71.0/exe/rubocop:12:in `<top (required)>'
/home/pocke/.rbenv/versions/trunk/bin/rubocop:23:in `load'
/home/pocke/.rbenv/versions/trunk/bin/rubocop:23:in `<main>'
Inspecting 1 file


0 files inspected, no offenses detected

---

This change will fix the problem.

---

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]

👍