Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6b7be0fb800b
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Merge pull request #22791 from Cwiiis/bug1048937-add-share-to-system-browser

Bug 1048937 - Implement  'share' option in system browser. r=vingtetun,kgrandon,jrburke

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https://hg.mozilla.org/integration/gaia-central/rev/adb138b84494
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 1048937 - Add test for share option in system browser. r=kgrandon,jrburke

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https://hg.mozilla.org/integration/gaia-central/rev/550d53a12127
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 1048937 - Implement  'share' option in system browser. r=vingtetun
Bumping manifests a=b2g-bump