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

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https://hg.mozilla.org/integration/gaia-central/rev/50497a869e33
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Merge pull request #13748 from AlinT/bug_938557

Bug 938557 - Write a test for finding a contact using the dialer

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https://hg.mozilla.org/integration/gaia-central/rev/5a4a44ac14aa
Author: AlinT <trifandreialin@gmail.com>
Desc: Bug 938557 - Write a test for finding a contact using the dialer

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https://hg.mozilla.org/integration/gaia-central/rev/85000840ebbb
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #15040 from julienw/956691-jshint-2.4.1

Bug 956691 - Upgrade jshint to 2.4.1 r=rik

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https://hg.mozilla.org/integration/gaia-central/rev/1f72d5273d06
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 956691 - Upgrade jshint to 2.4.1 r=rik