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

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https://hg.mozilla.org/integration/gaia-central/rev/26910dd4748d
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #20722 from cctuan/987487-3

Bug 987487 - [Gaia] [Build] Refactoring webapp-optimize.js and unit tests

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https://hg.mozilla.org/integration/gaia-central/rev/f8e049099101
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 987487 - [Gaia] [Build] Refactoring webapp-optimize.js and unit tests
Bumping manifests a=b2g-bump