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

========

https://hg.mozilla.org/integration/gaia-central/rev/6f275a4a3570
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #18748 from vsireesha246/Bug_1002445_Udating_Seekbar

Bug 1002445 - [video]Seekbar moves in player pause state r=john hu

========

https://hg.mozilla.org/integration/gaia-central/rev/1ed6afbb83f5
Author: varada.sireesha <varada.sireesha@lge.com>
Desc: Bug 1002445 - [video]Seekbar moves in player pause state

========

https://hg.mozilla.org/integration/gaia-central/rev/fd214b5c278e
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #18778 from ranjithgithub/1000050_GallerySectionUXChanges

Bug 1000050 - [Gallery][UX] Thumbnail selection header UX is not consistent, r=johu

========

https://hg.mozilla.org/integration/gaia-central/rev/4378af9e3a9f
Author: ranjith.gutha <ranjith.gutha@lge.com>
Desc: 1000050-changing section class name
Bumping manifests a=b2g-bump