Upgrade testing-related dependencies

[jgonggrijp]

I was warned by Sauce Labs that they are deprecating some older versions of their API, which made me realize I probably needed to upgrade karma-sauce-launcher. I decided to grasp the opportunity to upgrade more devDependencies. I'll be pushing the commits one by one to check that everything still works after every change.

[coveralls]

Coverage decreased (-0.2%) to 95.024% when pulling 6d93d6faf89f3b70dc03b3bfbe452d37a79efb1f on upgrade-sauce into a15d1afc708ec23894880b2ec4c1eb309447a906 on master.

[jgonggrijp]

Browser tests through Sauce Labs intermittently fail, for three reasons:

• Full page reloads in Firefox 11 for unknown reasons (probably a test framework compatibility issue).
• Temporary failure to establish a connection with Sauce Labs.
• The well-known, highly sporadic failure of the throttle/debounce reentrant tests, usually in old Edge or old Firefox.

The first reason is by far the most common, and I'll be documenting it in a new issue. The upgrades otherwise seem unproblematic and are quite necessary, so I'm still going to merge this.