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

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https://hg.mozilla.org/integration/gaia-central/rev/354111e5040b
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #18049 from etiennesegonzac/bug-993018-place-new-call-activity

Bug 993018 - Replace the "place new call" postMessages with a WebActivity r=rik

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https://hg.mozilla.org/integration/gaia-central/rev/47f5379c5cd4
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 993018 - Replace the "place new call" postMessages with a WebActivity
in order to remove a callscreen->appWindow dependency.
Bumping manifests a=b2g-bump