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

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https://hg.mozilla.org/integration/gaia-central/rev/31d028bfcc44
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #12236 from gasolin/issue-911696

Bug 911696 - [Dialer] [Flatfish] hide dialer app in homescreen if no tel..., r=crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/c0226574c7ea
Author: gasolin <gasolin@gmail.com>
Desc: Bug 911696 - [Dialer] [Flatfish] hide dialer app in homescreen if no telephony support