Bumping gaia.json for 2 gaia-central revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/c19a020a93a4
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #15321 from bobsilverberg/tbpl_system

Bug 957122 - Enable more TBPL tests - System app

========

https://hg.mozilla.org/integration/gaia-central/rev/b33660be6720
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Bug 957122 - Enable more TBPL tests - System app

Enable test_context_menu_activity_picker on TBPL