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

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https://hg.mozilla.org/integration/gaia-central/rev/6e202cf5ec49
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Merge pull request #18005 from EverythingMe/991674-icon-retriever-fail

Bug 991674 - IconRetriever fails to get icon but error callback is not e...

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https://hg.mozilla.org/integration/gaia-central/rev/8871e9721ee4
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 991674 - IconRetriever fails to get icon but error callback is not executed [r=crdlc]
Bumping manifests a=b2g-bump