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

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https://hg.mozilla.org/integration/gaia-central/rev/259568db63e1
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #19024 from huchengtw-moz/Stingray/Bug_1006378-selection-border

Bug 1006378 - [Stingray] Add selection border support to homescreen-stin..., r=garychen, r=lchang

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https://hg.mozilla.org/integration/gaia-central/rev/6833725517e6
Author: John Hu <johu@mozilla.com>
Desc: Bug 1006378 - [Stingray] Add selection border support to homescreen-stingray
Bumping manifests a=b2g-bump