Update build.gradle

* dependency upgrades: Google closure compiler v20130227, Spock 0.7
Merge pull request #64 from twwwt/patch-1

Upgrade Google Closure Compiler to v20130227
Add code coverage report
Update version and allow variable reporter for JSHint
Merge JSHint checkstyle feature from @levsa
Cherry picked b32efa5
Update README for v1.5.0
Merged with master