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

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https://hg.mozilla.org/integration/gaia-central/rev/861186d59a0e
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #18215 from jmcanterafonseca/fix_utils_config

Bug 994690 - Refactor config loader to use promises and add unit tests t...

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https://hg.mozilla.org/integration/gaia-central/rev/b64cde639b22
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 994690 - Refactor config loader to use promises and add unit tests to it
Bumping manifests a=b2g-bump