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

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https://hg.mozilla.org/integration/gaia-central/rev/f4459936dcab
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15597 from AndreiH/bug962504

Bug 962504 - Investigate intermittent fail on test_cost_control_reset_wi...

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https://hg.mozilla.org/integration/gaia-central/rev/fdbddb876685
Author: Andrei Hutusoru <andreihutusoru@P5069.(none)>
Desc: Bug 962504 - Investigate intermittent fail on test_cost_control_reset_wifi
Bumping manifests a=b2g-bump