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

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https://hg.mozilla.org/integration/gaia-central/rev/2599a455ca5b
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #20352 from yurenju/remove-test-agent-bootstrap

Bug 1016278 - get /test/unit/_proxy.html and _sandbox in httpd extension r=@timdream

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https://hg.mozilla.org/integration/gaia-central/rev/ea2b14d6d3d5
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1016278 - get /test/unit/_proxy.html and _sandbox in httpd extension
Bumping manifests a=b2g-bump