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

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https://hg.mozilla.org/integration/gaia-central/rev/cecf3657eeb4
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Merge pull request #16075 from gabrielesvelto/bug-967662

Bug 967662 - Recompress the PNG images added in bug 833401 r=kaze

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https://hg.mozilla.org/integration/gaia-central/rev/237e9bec6237
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 967662 - Recompress the PNG images added in bug 833401 r=kaze
Bumping manifests a=b2g-bump