chore(npm): update protractor to 4.0.0

4.0.0 is the first version with Selenium 2.53.x, and we need that as lower versions have problems
with current Firefox versions.
See SeleniumHQ/selenium#1202 and SeleniumHQ/selenium#2110.

We are currently running tests on FF28.

The breaking changes in 4.0.0 do not need action on our part.

Author: Narretz