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

Conflicts:
- README.md
  Kept our version
- app/javascript/mastodon/features/compose/components/compose_form.js
  Two changes too close to each other, took both changes

Gemfile.lock

@@ -271,7 +271,7 @@ GEM
     httplog (1.2.0)
       rack (>= 1.0)
       rainbow (>= 2.0.0)
-    i18n (1.5.2)
+    i18n (1.5.3)
       concurrent-ruby (~> 1.0)
     i18n-tasks (0.9.28)
       activesupport (>= 4.0.2)
@@ -457,7 +457,7 @@ GEM
       nokogiri (>= 1.6)
     rails-html-sanitizer (1.0.4)
       loofah (~> 2.2, >= 2.2.2)
-    rails-i18n (5.1.2)
+    rails-i18n (5.1.3)
       i18n (>= 0.7, < 2)
       railties (>= 5.0, < 6)
     rails-settings-cached (0.6.6)