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

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https://hg.mozilla.org/integration/gaia-central/rev/4988a710019c
Author: Yura Zenevich <yura.zenevich@gmail.com>
Desc: Merge pull request #20375 from yzen/bug-1023995

Bug 1023995 - fixing visibility issues around e.me.

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https://hg.mozilla.org/integration/gaia-central/rev/72212ada7ded
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1023995 - fixing visibility issues around e.me. r=ran
Bumping manifests a=b2g-bump
Bug 1026320 - Deal with race condition due to slow response from VolumeManager. r=qDot