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

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https://hg.mozilla.org/integration/gaia-central/rev/52b107b66f80
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15421 from KevinGrandon/bug_956648_bump_test_agent

Bug 956648 - Update test-agent version

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https://hg.mozilla.org/integration/gaia-central/rev/98c92fa488a6
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 956648 - Update test-agent version