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

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https://hg.mozilla.org/integration/gaia-central/rev/277260054912
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #15831 from crdlc/bug-964889

Bug 964889 - [B2G][Homescreen] Dock apps disappear after restarting devi...

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https://hg.mozilla.org/integration/gaia-central/rev/ce5a964b3e26
Author: crdlc <crdlc@tid.es>
Desc: Bug 964889 - [B2G][Homescreen] Dock apps disappear after restarting device with sim lock on and lock screen disabled
Bumping manifests a=b2g-bump