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

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https://hg.mozilla.org/integration/gaia-central/rev/4bd5115d9d78
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #12731 from alivedise/bugzilla/924553/mozapptype-match

Bug 924553 - Remove redundant string match, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/d3b1ee3c6d57
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 924553 - Remove redundant string match on mozapptype

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https://hg.mozilla.org/integration/gaia-central/rev/beeba3baacd5
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #12787 from gtorodelvalle/contacts-bug-924903-custom-tag-reloaded

Bug 924903 - [Contacts] Custom tag for mobile, email an address can be edited but it is not saved

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https://hg.mozilla.org/integration/gaia-central/rev/ca7be3bf53fe
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 924903 - [Contacts] Custom tag for mobile, email an address can be edited but it is not saved