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

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https://hg.mozilla.org/integration/gaia-central/rev/028e8cf5f316
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Merge pull request #18629 from arcturus/bug-991141

Bug 991141 - Look and feel for edit mode (list in select mode used for deleting)

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https://hg.mozilla.org/integration/gaia-central/rev/f2cd8595498d
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Bug 991141 - [Follow up from Bug 956219] Look and feel for "Delete contacts" button under Settings
Bumping manifests a=b2g-bump