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

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https://hg.mozilla.org/integration/gaia-central/rev/74dc8a91d9d4
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13947 from viorelaioia/bug_941731

Bug 941731 - Improve wait for http authentication dialog

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https://hg.mozilla.org/integration/gaia-central/rev/202fb296b89d
Author: Viorela Ioia <viorelaioia@gmail.com>
Desc: Bug 941731 - Improve wait for http authentication dialog