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

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https://hg.mozilla.org/integration/gaia-central/rev/31726553f82e
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #16938 from crdlc/bug-978011

Bug 978011 - Unload properly Image Loader when syncing/importing

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https://hg.mozilla.org/integration/gaia-central/rev/9d5c143246bc
Author: crdlc <crdlc@tid.es>
Desc: Bug 978011 - Unload properly Image Loader when syncing/importing
Bumping manifests a=b2g-bump