Bumping gaia.json for 4 gaia-central revision(s)

========

https://hg.mozilla.org/integration/gaia-central/rev/8df688ed76bc
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #11078 from cctuan/894802

Bug 894802 - [System] Status bar shows time when it is in lockscreen

========

https://hg.mozilla.org/integration/gaia-central/rev/a4a86ef00d2a
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 894802 - [System] Status bar shows time when it is in lockscreen

========

https://hg.mozilla.org/integration/gaia-central/rev/74272e5a462b
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #11081 from cctuan/master-system-fix

Bug 896231 - hdpi resolution tweaks update for System app

========

https://hg.mozilla.org/integration/gaia-central/rev/06219b995398
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 896231 - hdpi resolution tweaks update for System app