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

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https://hg.mozilla.org/integration/gaia-central/rev/53a8a9a7b4ed
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Merge pull request #15489 from dmarcos/bug961334

Bug 961334 - [Camera] Improving readability of code by getting rid of th...

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https://hg.mozilla.org/integration/gaia-central/rev/976163929a19
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Bug 961334 - [Camera] Improving readability of code by getting rid of the local variable proto
Bumping manifests a=b2g-bump