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

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https://hg.mozilla.org/integration/gaia-central/rev/795c9583c57b
Author: na-matsumoto <na-matsumoto@kddi-tech.com>
Desc: Bug 974878 - [MMS]Create new contact/ add to exist contact with email address r=julien

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https://hg.mozilla.org/integration/gaia-central/rev/2f01749fa20b
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #21493 from crdlc/bug-1033531

Bug 1033531 - [Vertical Homescreen] Apps dont appear in custom smart col...

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https://hg.mozilla.org/integration/gaia-central/rev/e9adb33bbcb8
Author: crdlc <crdlc@tid.es>
Desc: Bug 1033531 - [Vertical Homescreen] Apps dont appear in custom smart collections if Smart Collection is entered too quickly
Bumping manifests a=b2g-bump