Integrate jshint linting into travis build

This commit attempts to integrate linting via "jshint" into the "travis-ci" build process and introduces the following changes:

  + add a "jshint" entry to the "scripts" section of the "package.json"
  + update the ".travis.yml" to call "npm run-script jshint" before tests

Maybe you want to give it a try.. 

regards
~david