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

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https://hg.mozilla.org/integration/gaia-central/rev/f689accc02c5
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #18599 from gaye/calendar-visual-refresh

Bug 951069 - Month view visual refresh r=millermedeiros

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https://hg.mozilla.org/integration/gaia-central/rev/6c9259cd6e99
Author: gaye <gaye@mozilla.com>
Desc: Bug 951069 - Month view visual refresh
Bumping manifests a=b2g-bump