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

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https://hg.mozilla.org/integration/gaia-central/rev/a6ece290b974
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #15509 from steveck-chung/bug-950623

Bug 950623 - [Messages] Multi-recipient. Back button is kept as pressed after going back from recipients details list. r=julienw

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https://hg.mozilla.org/integration/gaia-central/rev/ed0fa41a84ec
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 950623 - [Messages] Multi-recipient. Back button is kept as pressed after going back from recipients details list
Bumping manifests a=b2g-bump