Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/8c47142a5b69
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #21333 from steveck-chung/bug-974867

Bug 974867 - [MMS]Auto suggestion for email address. r=steveck-chung

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https://hg.mozilla.org/integration/gaia-central/rev/436b18808449
Author: na-matsumoto <na-matsumoto@kddi-tech.com>
Desc: Bug 974867 - [MMS]Auto suggestion for email address. r=steveck-chung

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https://hg.mozilla.org/integration/gaia-central/rev/c5c40c82b9f3
Author: GaryChen, PYChen, Gary <mmm198219@gmail.com>
Desc: Merge pull request #21326 from begeeben/bug_1014487

Bug 1014487 - [build script] remove 'browser.homescreenURL' and 'browser.manifestURL'. r=yuren.

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https://hg.mozilla.org/integration/gaia-central/rev/c54d5916a5ee
Author: Yi-Fan Liao <begeeben@gmail.com>
Desc: Bug 1014487 - [build script] remove 'browser.homescreenURL' and 'browser.manifestURL'

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https://hg.mozilla.org/integration/gaia-central/rev/61f17401e8e8
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #21353 from julienw/1033221-debug-mozilla-download

Bug 1033221 - Add more debug to mozilla-download r=@yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/224c20d25c0b
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1033221 - Add more debug to mozilla-download r=yurenju
Bumping manifests a=b2g-bump