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

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https://hg.mozilla.org/integration/gaia-central/rev/d02fb7920a67
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15901 from crdlc/bug-966889

Bug 966889 - Browser System App is Deletable

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https://hg.mozilla.org/integration/gaia-central/rev/cb175d14d094
Author: crdlc <crdlc@tid.es>
Desc: Bug 966889 - Browser System App is Deletable
Bumping manifests a=b2g-bump