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

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https://hg.mozilla.org/integration/gaia-central/rev/0284cd20f534
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #15068 from comoyo/newkb_tests

Bug 956169 - Unit tests for new keyboard r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/9696edd8d247
Author: Jan Jongboom <janjongboom@gmail.com>
Desc: Bug 956169 - Unit tests for shiftkey.js and doublespace.js

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https://hg.mozilla.org/integration/gaia-central/rev/026a9cb9501a
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #15240 from davidflanagan/bug956170

Bug 956170: implement new visuals for refactored keyboard

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https://hg.mozilla.org/integration/gaia-central/rev/71a8be226d2d
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 956170: implement new visuals for refactored keyboard

visual tweaks based on review comments
Bumping manifests a=b2g-bump