Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- `Gemfile`:
  We updated httplog in a separate commit.
  Took upstream's change which updated it further.
- `Gemfile.lock`:
  We updated httplog in a separate commit.
  Took upstream's change which updated it further.
- `app/lib/sanitize_config.rb`:
  Upstream added better unsupported link stripping,
  while we had different sanitizing configs.
  Took only upstream's link stripping code.
- `config/locales/simple_form.pl.yml`:
  Strings unused in glitch-soc had been removed from
  glitch-soc, reintroduced them even if they are not
  useful, to reduce the risk of later merge conflicts.

lib/mastodon/version.rb

@@ -17,7 +17,7 @@ module Mastodon
     end
 
     def flags
-      'rc2'
+      ''
     end
 
     def suffix