Gradle version and Scala page updates.

Updated Gradle version site-wide. It was sometimes 1.0 and sometimes 1.3. Current version is 1.4 per: https://github.com/travis-ci/travis-cookbooks/commit/fb9bc697b92a8eeacdca3626ce71f214ce959302

Updated the Scala page to include new information about Gradle building and testing per: https://github.com/travis-ci/travis-build/commit/d70c9098719fa53e01bf6f854d2e569d100d8e5d

Also took the opportunity to clean up the Scala page to closely match the structure/flow of the Groovy page.