Update to version 0.6-brewdev1

This isn't a named upstream version, but the currently tagged version of
MDK has multiple bugs which really dimish the value of it:

* mdk behat is completely broken
* The jira patch integration is broken
* composer is not used for phpunit versions <25

So homebrew users - we are on the bleeding edge. The good news is the
bleeding edge is much less buggy than the 'stable' version.