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

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https://hg.mozilla.org/integration/gaia-central/rev/431ea8ef9f12
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13900 from zacc/bug_941427

Bug 941427 - Strengthen is_displayed() and wait for it before dismissing ...

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https://hg.mozilla.org/integration/gaia-central/rev/b923b0c960a4
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 941427 - Strenthen is_displayed() and wait for it before dismissing keyboard