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

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https://hg.mozilla.org/integration/gaia-central/rev/3fdf71c424e9
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #20970 from yurenju/settings-remove-makefile

Bug 1029966 - rewrite settings build script in javascript r=@ochameau

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https://hg.mozilla.org/integration/gaia-central/rev/ed879763d781
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1029966 - rewrite settings build script in javascript
Bumping manifests a=b2g-bump