Release 1.6.0
Update to version 1.7.0-pre

[ci skip]
Roll back wd to 0.2.2

The `waitForElementX` methods in wd 0.2.11 return an element (and
therefore set the context) which can break existing functional tests.
Update sauce-connect-launcher to 0.4.0

sauce-connect-launcher 0.4.0 uses Sauce Connect 4.1, which includes
new Sauce Labs SSL certificates.

resolves #175, #176
Improve error reporting of proxy message duplicates
Fix proxy tries to read directories as files
Fix error messages are being double-logged
Fix setHeartbeatInterval is not chainable
Fix uncaught exceptions in runner being silently discarded
Fix config files being loaded from the wrong location
Style convention fix
[WIP] Normalize console reporter error display
Source address parsing bugfix
Use my modified istanbul as the dependency
[WIP] Stack traces are normalized and corrected

Stack traces are mostly normalized between different browsers. Stack
trace lines are updated based on instrumentation source map data if
available.