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

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https://hg.mozilla.org/integration/gaia-central/rev/521becff4b09
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #19230 from cctuan/1010111

Bug 1010111 - [Build] utils.Commander cannot init path in string format

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https://hg.mozilla.org/integration/gaia-central/rev/fd668ea058a9
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1010111 - [Build] utils.Commander cannot init path in string format
Bumping manifests a=b2g-bump