When trying to `require` a gem running in an unlinked directory, an exception is
thrown because `Dir.pwd` is called (see rubygems/rubygems#3087).
Until the fix lands in an official release, we monkey patch `Dir.pwd` to return
'/' if a `Errno::ENOENT` exception is raised while loading the colorls gem.
This should work for all Unixes. On Windows, this error cannot happen since you
cannot unlink a directory which is still in use by a process.
Fixes#351.
It reached EOL on 20th Jun 2018 and no longer receives patches.
* set required Ruby version to >= 2.3 in spec file
* set rubocop's TargetRubyVersion to 2.3 and fix all the offenses
