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

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https://hg.mozilla.org/integration/gaia-central/rev/8504bb3813e1
Author: viorelaioia <viorela.ioia@softvision.ro>
Desc: Merge pull request #25816 from bebef1987/clear

Bug 1093131 - Add a test that delete browser's history

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https://hg.mozilla.org/integration/gaia-central/rev/e4698bb131cb
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 1093131 - Add a test that delete browser's history
Bumping manifests a=b2g-bump