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

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https://hg.mozilla.org/integration/gaia-central/rev/4e31820d7b6e
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #18201 from etiennesegonzac/instacallscreen

Bug 990003 - Introducing a dedicated callscreen app for better performance r=rik, alive, 21

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https://hg.mozilla.org/integration/gaia-central/rev/414db68d7a2c
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 990003 - Introducing a dedicated callscreen app for dramatically
improved performances.
Bumping manifests a=b2g-bump