Bumping gaia.json for 4 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/d573cf3fff64
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #10628 from etiennesegonzac/bug-879966-voicemail-icon

Bug 879966 - Better voicemail notification icon.

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https://hg.mozilla.org/integration/gaia-central/rev/a5b48ca2cc80
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 879966 - Better voicemail notification icon.
r=samjoch

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https://hg.mozilla.org/integration/gaia-central/rev/991ff233d69a
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #10496 from siemiatj/bug_829406

Bug 829406 - Dialer doesn't send tones when user leaves the button r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/963d3be5c988
Author: jakub <jakub@bryntum.com>
Desc: Bug 829406 - Dialer doesn't send tones when user leaves the button before releasing it.