Bug 1275843: Bump Marionette driver to v2.0.0 r=maja_zf

Since we have changed the way that get_attribute returns things and
we have added get_property it makes sense to have this as a major
release.

MozReview-Commit-ID: 5ANGYVLUe8k

--HG--
extra : rebase_source : 6ebaf9f23cf2c043ffccff877fbfea2533b95dde

testing/marionette/client/marionette_driver/__init__.py

@@ -2,7 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-__version__ = '1.4.0'
+__version__ = '2.0.0'
 
 from marionette_driver import (
     addons,