Bumping gaia.json for 2 gaia-1_3 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_3/rev/b7ad61d57921
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #15396 from huchengtw-moz/system/Bug_959283_activity_window_factory_v1.3

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

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https://hg.mozilla.org/integration/gaia-1_3/rev/42dd7b8873a4
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