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

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https://hg.mozilla.org/integration/gaia-central/rev/b644d4a497d3
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #24784 from scriptofer/master

Bug 996332 - Fix Switch back to alphabets after @ is typed, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/77478fe2a4df
Author: scriptofer <scriptofer@gmail.com>
Desc: Bug 996332 - Fix Switch back to alphabets after @ is typed R=scriptofer
Bumping manifests a=b2g-bump