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

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https://hg.mozilla.org/integration/gaia-central/rev/9d42b77320ed
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #18784 from rnowm/1000132

Bug 1000132 - [Building Blocks] Split headers.css to demo @import r=cyee

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https://hg.mozilla.org/integration/gaia-central/rev/5d8904e5e8c6
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 1000132 - [Building Blocks] Split headers.css to demo @import
Bumping manifests a=b2g-bump