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

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https://hg.mozilla.org/integration/gaia-central/rev/387dd3872cf8
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #21343 from cctuan/1027534

Bug 1027534 - [System][Test] Integration test for inline->window activity call chain

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https://hg.mozilla.org/integration/gaia-central/rev/bdeb15e02b47
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1027534 - [System][Test] Integration test for inline->window activity call chain
Bumping manifests a=b2g-bump