Goodbye Travis CI, hello Circle CI? (fixes #559)

.travis.yml

-language: ruby
-cache:
-  bundler: true
-  yarn: true
-  directories:
-    - node_modules
-    - public/assets
-    - public/packs-test
-    - tmp/cache/babel-loader
-dist: trusty
-sudo: false
-
-notifications:
-  email: false
-
-env:
-  global:
-    - LOCAL_DOMAIN=cb6e6126.ngrok.io
-    - LOCAL_HTTPS=true
-    - RAILS_ENV=test
-    - PARALLEL_TEST_PROCESSORS=2
-    - ALLOW_NOPAM=true
-
-addons:
-  postgresql: 9.4
-  apt:
-    sources:
-      - trusty-media
-      - sourceline: deb https://dl.yarnpkg.com/debian/ stable main
-        key_url: https://dl.yarnpkg.com/debian/pubkey.gpg
-    packages:
-      - ffmpeg
-      - libicu-dev
-      - libprotobuf-dev
-      - protobuf-compiler
-      - yarn
-
-rvm:
-  - 2.4.3
-  - 2.5.1
-
-services:
-  - redis-server
-
-install:
-  - nvm install
-  - bundle install --path=vendor/bundle --with pam_authentication --without development production --retry=3 --jobs=16
-  - yarn install
-
-# https://github.com/travis-ci/travis-ci/issues/9333
-before_install:
-  - gem install bundler
-
-before_script:
-  - travis_wait ./bin/rails parallel:create parallel:load_schema parallel:prepare assets:precompile
-  - yarn install --no-progress
-
-script:
-  - travis_retry bundle exec parallel_test spec/ --group-by filesize --type rspec
-  - yarn run test:jest
-  - bundle exec i18n-tasks check-normalized && bundle exec i18n-tasks unused