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

========

https://hg.mozilla.org/integration/gaia-central/rev/873b197d2cdf
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #16904 from zacc/bug_979253

Bug 979253 - Remove deprecated LockScren class from gaiatest

========

https://hg.mozilla.org/integration/gaia-central/rev/e787a98c4f6e
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 979253 - Remove deprecated LockScren class from gaiatest
Bumping manifests a=b2g-bump