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

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https://hg.mozilla.org/integration/gaia-central/rev/db887588719d
Author: Carmen Jiménez <cjc@tid.es>
Desc: Merge pull request #19229 from mcjimenez/bug1010088

Bug 1010088 - Use STAGE_DIR consistently on build process

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https://hg.mozilla.org/integration/gaia-central/rev/61ee7307ff7b
Author: Carmen Jimenez Cabezas <cjc@tid.es>
Desc: Bug 1010088 - Use STAGE_DIR consistently on build process
Bumping manifests a=b2g-bump