upgrade(rails 5): no longer use rake to invoke rake tasks, use rails

though I left the case alone where the command would previously been
just `bundle exec rake`, as doing the same doesn't work for rails.

.travis.yml

@@ -11,8 +11,8 @@ before_install:
   - "if [ $(phantomjs --version) != '2.1.1' ]; then tar -xvf ${PWD}/travis_phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2 -C ${PWD}/travis_phantomjs; fi"
   - "phantomjs --version"
 
-before_script: rake db:setup
-before_script: bundle exec rake db:setup
+before_script: rails db:setup
+before_script: bundle exec rails db:setup
 cache: bundler
 sudo: false
-env: RAILSGOAT_MAINTAINER=true
+env: RAILSGOAT_MAINTAINER=true