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

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https://hg.mozilla.org/integration/gaia-central/rev/e26778bc9357
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #13922 from caseyyee/bug-941772

Bug 941772: [Building Blocks] Fix header right-aligned text button color...

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https://hg.mozilla.org/integration/gaia-central/rev/282ef9dbc4a6
Author: Casey Yee <casey@caseyyee.com>
Desc: Bug 941772: [Building Blocks] Fix header right-aligned text button colors