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

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https://hg.mozilla.org/integration/gaia-central/rev/3c91459ab1c3
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #20397 from jimporter/email-as-user-agent

Bug 880670 - [email/activesync] some ActiveSync implementations blacklis...

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https://hg.mozilla.org/integration/gaia-central/rev/05cb5f527ee9
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 880670 - [email/activesync] some ActiveSync implementations blacklist Mozilla in the user-agent string and return a 440 status code
Bumping manifests a=b2g-bump