Conflicts:
- `CONTRIBUTING.md`:
  Upstream file has changed and we're quoting it.
  Ported the changes.
- `README.md`:
  Upstream file has changed but we have a completely different one.
  Kept our version.
- `lib/mastodon/version.rb`:
  Upstream has changed from `tootsuite/mastodon` to `mastodon/mastodon`,
  but we're still `glitch-soc/mastodon`.
  Kept our version.
- `spec/presenters/instance_presenter_spec.rb`:
  Upstream has changed from `tootsuite/mastodon` to `mastodon/mastodon`,
  but we're still `glitch-soc/mastodon`.
  Kept our version.