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

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https://hg.mozilla.org/integration/gaia-central/rev/4fa04874d5e8
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #18317 from cctuan/983573-new

bug 983573 - [Gaia] Refactoring webapp-manifest.js

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https://hg.mozilla.org/integration/gaia-central/rev/e4ce659610e2
Author: cctuan <georgeiscoming@gmail.com>
Desc: bug 983573 - [Gaia] Refactoring webapp-manifest.js
Bumping manifests a=b2g-bump