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

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https://hg.mozilla.org/integration/gaia-central/rev/6ea60186e138
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #16151 from jimporter/ringtones-merge

Bug 960329 - [User story] Set a ringtone from a song in the music app

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https://hg.mozilla.org/integration/gaia-central/rev/6a278aefb27b
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 960329: Rewrite the ringtones app and allow sharing/deleting; r=djf, r=dkuo, r=yurenju, ui-r=tif, ui-r=chuang
Thanks also to Dominic Kuo and Punam Dahiya for patches which have been incorporated into this
Bumping manifests a=b2g-bump