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

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https://hg.mozilla.org/integration/gaia-central/rev/f7a78194ae8e
Author: Rick Waldron <waldron.rick@gmail.com>
Desc: Bug 951339 - [Messages][Drafts] Existing thread drafts not properly populated when a new message is sent to that same recipient r=julienw

https://bugzilla.mozilla.org/show_bug.cgi?id=951339
Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

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https://hg.mozilla.org/integration/gaia-central/rev/25b217bf4c6f
Author: Rick Waldron <waldron.rick@gmail.com>
Desc: Bug 952225 - [Messages][Drafts] Support subject line in message drafts r=julienw

https://bugzilla.mozilla.org/show_bug.cgi?id=952225
Signed-off-by: Rick Waldron <waldron.rick@gmail.com>