Bumping gaia.json for 3 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/290fc4628fbf
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 921827 - Split media file list into types. r=zcampbell

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https://hg.mozilla.org/integration/gaia-central/rev/b2ea1952ec7d
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #12442 from crdlc/bug-914115

Bug 914115 - [e.me][feature] Homescreen will expose an API to rename icons

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https://hg.mozilla.org/integration/gaia-central/rev/c5d326e8d6ea
Author: crdlc <crdlc@tid.es>
Desc: Bug 914115 - [e.me][feature] Homescreen will expose an API to rename icons