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

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https://hg.mozilla.org/integration/gaia-central/rev/5a4f3a3e1dd4
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 945774 - Remove xfail from test_sms_with_attachments r=me

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https://hg.mozilla.org/integration/gaia-central/rev/d96add071902
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 948468 - xfail test_dialer_add_contact with bug 947317 r=me