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

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https://hg.mozilla.org/integration/gaia-central/rev/b893c1aff49e
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #24866 from cctuan/1078707

Bug 1078707 - Closing apps no longer works via DevTools

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https://hg.mozilla.org/integration/gaia-central/rev/53756c24efc2
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1078707 - Closing apps no longer works via DevTools
Bumping manifests a=b2g-bump