Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/15291949ab37
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #24369 from mancas/bug1071312

Bug 1071312 - [FTU][FxA] Button still reads as 'Skip' after the user log...r=fcampo

========

https://hg.mozilla.org/integration/gaia-central/rev/72d8be1e4646
Author: Manuel Casas Barrado <manuel.casasbarrado@telefonica.com>
Desc: Bug 1071312 - [FTU][FxA] Button still reads as 'Skip' after the user logs into a Firefox Account in the FTE.

========

https://hg.mozilla.org/integration/gaia-central/rev/4945e4a3462c
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #22655 from anefzaoui/bug-964037

Bug 964037 - (gaia-rtl) Support RTL for Lockscreen App. r=alive

========

https://hg.mozilla.org/integration/gaia-central/rev/172902a0f2a1
Author: Ahmed Nefzaoui <nefzaoui.ahmed@hotmail.com>
Desc: Bug 964037 - (gaia-rtl) Support RTL for Lockscreen App
Bumping manifests a=b2g-bump