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

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https://hg.mozilla.org/integration/gaia-central/rev/e81ec57d689f
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Merge pull request #14047 from asutherland/stream-review

Bug 871897 - [email] Change mail sending process to use streaming to reduce peak memory usage. r=mcav

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https://hg.mozilla.org/integration/gaia-central/rev/d9cf0d0477c7
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Bug 871897 - [email] Change mail sending process to use streaming to reduce peak memory usage. r=mcav