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

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https://hg.mozilla.org/integration/gaia-central/rev/48c3449cd63e
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #17688 from elefant/bug/980814

Bug 980814 - Set system message handler when the test app is completely loaded.

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https://hg.mozilla.org/integration/gaia-central/rev/529830401243
Author: hchang <hchang@mozilla.com>
Desc: Bug 980814 - Set system message handler when the test app is completely loaded.
Bumping manifests a=b2g-bump