Bumping gaia.json for 1 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/519ab8808210
Author: Ran Ben Aharon <ran@ranbena.com>
Desc: Bug 934768 - [e.me] API key change for v1.2 [r=crdlc]