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

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https://hg.mozilla.org/integration/gaia-central/rev/999353866b7c
Author: Rudy Lu <me@rudy.lu>
Desc: Merge pull request #15792 from RudyLu/keyboard/Bug920431-keyboard_layout_customize_2

Bug 913782 - [Keyboard] Build time default keyboard selection work for
r=yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/dc3f38c67046
Author: Rudy Lu <me@rudy.lu>
Desc: Bug 913782 - [Keyboard] Build time default keyboard selection work for
3rd-party keyboard support
 - make build/settings.js read the default keyboard layout config

Bug 920431 - [keyboard] keyboard_layout.json should be customizable
  - Refine to make it adopt the config in distribution package
Bumping manifests a=b2g-bump