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

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https://hg.mozilla.org/integration/gaia-central/rev/c1056aff716d
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #16052 from millermedeiros/917536-enable_modify_event_test

Bug 917537 - Turn back on modify_event_test.js it was disabled because of intermittent failures

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https://hg.mozilla.org/integration/gaia-central/rev/12a753148e92
Author: Miller Medeiros <miller@millermedeiros.com>
Desc: Bug 917537 - Turn back on modify_event_test.js it was disabled because of intermittent failures
Bumping manifests a=b2g-bump