Upgrade Babel to version 7.0.0 (#5925)

.babelrc

Gemfile

Gemfile.lock

...on/components/__tests__/__snapshots__/button-test.js.snap

app/javascript/mastodon/components/account.js

app/javascript/mastodon/components/column_header.js

app/javascript/mastodon/components/domain.js

app/javascript/mastodon/components/load_gap.js

app/javascript/mastodon/components/media_gallery.js

app/javascript/mastodon/components/relative_timestamp.js

app/javascript/mastodon/components/status.js

app/javascript/mastodon/components/status_action_bar.js

...script/mastodon/features/account/components/action_bar.js

...javascript/mastodon/features/account/components/header.js

app/javascript/mastodon/features/account_gallery/index.js

app/javascript/mastodon/features/account_timeline/index.js

app/javascript/mastodon/features/blocks/index.js

...features/community_timeline/components/column_settings.js

app/javascript/mastodon/features/community_timeline/index.js

...script/mastodon/features/compose/components/action_bar.js