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

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https://hg.mozilla.org/integration/gaia-central/rev/9a54560dc4ee
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #15749 from RickyChien/issue-957932

Bug 957932 - Add coverage checkbox for test-agent web interface r=@yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/a590b5e09cc4
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 957932 - Add coverage checkbox for test-agent web interface

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https://hg.mozilla.org/integration/gaia-central/rev/564a17bb99cf
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #15752 from cctuan/950185-2

Bug 950185 - [B2G] [Settings] Network type does not show user friendly o...

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https://hg.mozilla.org/integration/gaia-central/rev/c0fb371b27a1
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 950185 - [B2G] [Settings] Network type does not show user friendly options such as 2G and 3G
Bumping manifests a=b2g-bump