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

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https://hg.mozilla.org/integration/gaia-central/rev/911dce24602d
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #18449 from gasolin/issue-993832

Bug 993832 - wrong multi-res resource file name, r=yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/83d423571bae
Author: gasolin <gasolin@gmail.com>
Desc: Bug 993832 - wrong multi-res resource file name
Bumping manifests a=b2g-bump