Merge remote-tracking branch 'upstream/master' into pipeline-emails

* upstream/master: (372 commits)
  Enable Lint/StringConversionInInterpolation cop and autocorrect offenses
  resolve duplicated changelog entry
  credit myself 
  change determine conditions
  override subject method in devise mailer
  follow the styleguide: Don't use parentheses around a literal
  wrap subject with method subject
  move spec back into shared example `an email sent from GitLab`
  stub config settings in spec
  remove empty line at block body end
  remove extra entry
  create new test in `spec/mailers/notify_spec.rb`
  move changelog to 8.13
  add configurable email subject suffix
  Fixes sidebar navigation.
  Convert "SSH Keys" Spinach features to RSpec
  Enable import/export back for non-admins
  Update gitlab-shell to 3.6.3
  Updated artwork of empty group state.
  Better empty state for Groups view.
  ...