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

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https://hg.mozilla.org/integration/gaia-central/rev/66cf75ccef9c
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #16446 from psingapati/Bug_965139_WiFiWakeLock_Email_Send

Bug 965139 - [Email] Acquiring a wifi wakelock while sending an email r=jrburke

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https://hg.mozilla.org/integration/gaia-central/rev/28385a8660cc
Author: praveen.singapati <praveen.singapati@lge.com>
Desc: Bug 965139 - [Email] Acquiring a wifi wakelock while sending an email

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Bumping manifests a=b2g-bump