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

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https://hg.mozilla.org/integration/gaia-central/rev/6946a71605af
Author: Mihai Cîrlănaru <mihai@cirlanaru.com>
Desc: Merge pull request #15505 from mihai/bug_937975

Bug 937975 - [Settings] Add title for USB storage confirm dialog, r=@crh0716

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https://hg.mozilla.org/integration/gaia-central/rev/4f1be5e6446c
Author: Mihai Cirlanaru <mihai@cirlanaru.com>
Desc: Bug 937975 - [Settings] Add title for USB storage confirm dialog. r=arthurcc
Bumping manifests a=b2g-bump