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 https://github.com/SeleniumHQ/selenium/issues/1202 and https://github.com/SeleniumHQ/selenium/issues/2110.

We are currently running tests on FF28.

As part of the update the deprecated webdriver fn getInnerHtml has been replaced with getAttribute('innerHTML')