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

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https://hg.mozilla.org/integration/gaia-2_0/rev/f4a90460b8c7
Author: James Lal <james@lightsofapollo.com>
Desc: Bug 1022094 - Add test to cover appcache installed download case a=test-only

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https://hg.mozilla.org/integration/gaia-2_0/rev/50e38c622e1d
Author: Ran Ben Aharon <ran@ranbena.com>
Desc: Bug 1023312 - [Vertical homescreen] Smart collection viewing fails on the flame because e.me server fails to return background. [r=amirn]
Bumping manifests a=b2g-bump