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

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https://hg.mozilla.org/integration/gaia-central/rev/647c6e6a226f
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #16620 from zacc/bug_976174

Bug 976174 - Better failure message in switch_to_keyboard() and dismiss(...

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https://hg.mozilla.org/integration/gaia-central/rev/09baf767d5cd
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 976174 - Better failure message in switch_to_keyboard() and dismiss()
Bumping manifests a=b2g-bump