Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-2_0/rev/c95828965ec8
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 1038578 - [Collection App] Icons are not updated after installing hosted apps from marketplace

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https://hg.mozilla.org/integration/gaia-2_0/rev/8761daeef551
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 1039311 - [Collection] HomeIcons Singleton (refactor)

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https://hg.mozilla.org/integration/gaia-2_0/rev/e21733544dce
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 1029977 - Do not use data-uris for collection backgrounds

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https://hg.mozilla.org/integration/gaia-2_0/rev/224a6aa371cb
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 1016221 - [Collection App] Mozilla CDN Backgrounds for Collection icons
Bumping manifests a=b2g-bump