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

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https://hg.mozilla.org/integration/gaia-central/rev/2721b92456e6
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #18111 from AndreiH/985498

Bug 985498 - Investigate and fix test_delete_app fail on Travis

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https://hg.mozilla.org/integration/gaia-central/rev/1c3defebc79a
Author: Andrei Hutusoru <andreihutusoru@P5069.(none)>
Desc: Bug 985498 - Investigate and fix test_delete_app fail on Travis

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https://hg.mozilla.org/integration/gaia-central/rev/604783362d20
Author: gitmai <mri@tid.es>
Desc: Merge pull request #18104 from gitmai/bug-986833-cc-app-msg-no-api

Bug 986833 - The cost control app doesn't work on b2g-desktop
r=salva

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https://hg.mozilla.org/integration/gaia-central/rev/7faec054cee6
Author: mai <mri@tid.es>
Desc: Bug 986833 - The cost control app doesn't work on b2g-desktop
Bumping manifests a=b2g-bump