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

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https://hg.mozilla.org/integration/gaia-central/rev/13d91fc76332
Author: RickyChien <ricky060709@gmail.com>
Desc: Merge pull request #16891 from RickyChien/bug-972699

Bug 972699 - Fix unit test zero coverage when using lazy load r=@yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/20cf28b60560
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 972699 - Fix unit test zero coverage when using lazy load
Bumping manifests a=b2g-bump