Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/72a7f5cea568
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 1038103 - Generate documentation from source code and publish to readthedocs.org. r=wlachance r=zcampbell
Bumping manifests a=b2g-bump