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

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https://hg.mozilla.org/integration/gaia-central/rev/4a8dcbcad943
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12819 from wanderview/video-test-require

Bug 924233: Add missing requires to video tests.  r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/722093280296
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 924233: Add missing requires to video tests.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "a541491b1762c14cb00b6fbc006024d60556e229", 
+    "revision": "4a8dcbcad9433e7cb0b619d80b041219e5946130", 
     "repo_path": "/integration/gaia-central"
 }