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

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https://hg.mozilla.org/integration/gaia-1_4/rev/c6f190cb6867
Author: Ben Tian <btian@mozilla.com>
Desc: Merge pull request #18727 from bentian/bug-997578-14

Bug 997578 - [1.4] Answer incoming call after hanging up active call, r=etienne, a=1.4+

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https://hg.mozilla.org/integration/gaia-1_4/rev/7a0ee71c3319
Author: Ben Tian <btian@mozilla.com>
Desc: Bug 997578 - [1.4] Answer incoming call after hanging up active call, a=1.4+
Bumping manifests a=b2g-bump