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

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https://hg.mozilla.org/integration/gaia-central/rev/e022eb54f8a6
Author: Jonathan Griffin <jgriffin@mozilla.com>
Desc: Merge pull request #12865 from jonallengriffin/fixreturncode

Bug 927097 - Set a non-zero exit code if any tests failed, r=ahal, a=test-only

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https://hg.mozilla.org/integration/gaia-central/rev/21c739ab7454
Author: Jonathan Griffin <jgriffin@mozilla.com>
Desc: Bug 927097 - Set a non-zero exit code if any tests failed, r=ahal, a=test-only

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https://hg.mozilla.org/integration/gaia-central/rev/993293ea0af7
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #12842 from alivedise/bugzilla/919864_master/screenshot-objecturl-leak

Bug 919864 - Better screenshot objectURL management to avoid mem leak, r=timdream, a=koi+

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https://hg.mozilla.org/integration/gaia-central/rev/6e24ba9e26af
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 919864 - Better screenshot objectURL management to avoid mem leak