Fix JSHint error

lib/observable.js: line 33, col 36
  Expected a conditional expression and instead saw an assignment.
Add package.json and dev dependencies

Now to run make's test and jshint tasks you can install dependencies using
npm install.
Merge pull request #72 from fork-n-roll/feature/fix-jshint-error

Fix JSHint error
Merge pull request #73 from fork-n-roll/feature/add-package.json

Add package.json and dev dependencies