fix(plook): make findURLs() properly resolve its promise

After the lookup was made, findURLs() was not resolving with the
possible found URLs.
chore(devDependencies): include sinon for tests
chore(test): create global for sinon and bower

To allow easier suite setup.
chore(jshint): add predefined vars in test env

Set 'bower', 'sinon' and 'afterEach' as globals as well
test(plook): fully test .lookup() and .findURLs()