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

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https://hg.mozilla.org/integration/gaia-central/rev/dd6dc50d5f1b
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13047 from zacc/bug_929636

Bug 929636 - Changed skipped Python UI tests to use fail-if

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https://hg.mozilla.org/integration/gaia-central/rev/c7bcbefa72ea
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 929636 - Changed skipped Python UI tests to use fail-if