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

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https://hg.mozilla.org/integration/gaia-central/rev/9cd510f97724
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #15397 from huchengtw-moz/system/Bug_959283_activity_window_factory

Bug 959283 - [B2G][Bluetooth File Transfer] On bluetooth transfer of mul..., r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/2179f7e82bef
Author: John Hu <johu@mozilla.com>
Desc: Bug 959283 - [B2G][Bluetooth File Transfer] On bluetooth transfer of multiple images opening concurrent recieved pictures through notification bar results in a blank gallery screen