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

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https://hg.mozilla.org/integration/gaia-1_4/rev/28500e06837b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #17468 from mikehenrty/bug-986721-aurora

Bug 986721 - Integration Tests in 1.4 should run against Aurora builds of b2g-desktop

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https://hg.mozilla.org/integration/gaia-1_4/rev/d570c02a2888
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 986721 - Integration Tests in 1.4 should run against Aurora builds of b2g-desktop
Bumping manifests a=b2g-bump