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

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https://hg.mozilla.org/integration/gaia-central/rev/dddeb30f3845
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17631 from gasolin/issue-971515-2

Bug 971515 - [System2] Instantiable MediaRecording, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/f029aa859187
Author: gasolin <gasolin@gmail.com>
Desc: Bug 971515 - [System2] Instantiable MediaRecording
Bumping manifests a=b2g-bump