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

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https://hg.mozilla.org/integration/gaia-central/rev/3bb28013057e
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #17250 from eliperelman/bug-979396-homescreen-swipe-velocity

Bug 979396 - Converting homescreen swipe animation to be velocity-sensitive

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https://hg.mozilla.org/integration/gaia-central/rev/e6d4335cf06a
Author: Eli Perelman <eli@eliperelman.com>
Desc: Converting homescreen swipe animation to be velocity-sensitive

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "branch": "", 
         "revision": ""
     }, 
-    "revision": "2f64eeaddcd87ed3320adab071f84aaa20fdb2a6", 
+    "revision": "3bb28013057ebd86072df891a0af68fae540743f", 
     "repo_path": "/integration/gaia-central"
 }