Bumping gaia.json for 2 gaia-1_3 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_3/rev/fa4d35abdb78
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Merge pull request #15337 from asutherland/uplift-slice-batching

Bug 862870 - [email] Implement slice batching to reduce/minimize UI reflows, improve responsiveness, sync time. r=asuth, a=blocking-b2g=1.3+ Uplift

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https://hg.mozilla.org/integration/gaia-1_3/rev/8eb09bcac075
Author: Andrew Sutherland <asutherland@asutherland.org>
Desc: Merge pull request #15327 from asutherland/mail-slice-batching

Bug 862870 - [email] Implement slice batching to reduce/minimize UI reflows, improve responsiveness, sync time. r=asuth