Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_4/rev/ffb1f16b8ca2
Author: Francisco Jordano <fjordano@mozilla.com>
Desc: Bug 1012845 - [B2G][Gallery] When deleting downloaded images from the download settings, the image will not delete
Bumping manifests a=b2g-bump