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

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https://hg.mozilla.org/integration/gaia-central/rev/4de7d283e752
Author: Albert <acperez@tid.es>
Desc: Merge pull request #20188 from acperez/bug-1009633

Bug 1009633 - Pre-polulate browser top sites by SIM

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https://hg.mozilla.org/integration/gaia-central/rev/9084e9b4c47f
Author: Albert <acperez@tid.es>
Desc: Bug 1009633 - Pre-polulate browser top sites by SIM
Bumping manifests a=b2g-bump