Update mocha spec_helper.js template to use the new API of chai for chai.expect and chai.assert.

According to http://chaijs.com/, assert and expect shouldn't be called as a function. This was breaking initial Teaspoon installation when choose JavaScript to spec_helper.
Merge pull request #167 from sadjow/update-mocha-spec-helper

Update mocha spec_helper.js template to use the new API of chai.