Modifies JSHint config to enable new Ember e2e tests syntax

There is a new e2e tests syntax in new Ember version (see http://emberjs.com/guides/testing/integration/#toc_writing-tests). Before all methods were chained: `visit(...).click(...).then(...);` now they can be used separately: `visit(...); click(...); andThen(...);`. The implication of this new syntax is that more methods are global now (previously only `visit`, now also `click`, `andThen` etc.). This PR modifies JSHint config so it doesn't complain about these new global methods.