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

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https://hg.mozilla.org/integration/gaia-central/rev/908b97f474d9
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #16562 from yurenju/bug974070

Bug 974070 - [build system] install-gaia fails to kill the app when ther... r=@yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/f31a6a5e4593
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 974070 - [build system] install-gaia fails to kill the app when there is a SEC column (peak)
Bumping manifests a=b2g-bump