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

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https://hg.mozilla.org/integration/gaia-central/rev/686f7e5027bd
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #10930 from eeejay/lockscreen-elastic-fix

Bug 892649 - Make sure elastic is never played when screen reader is enabled r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/024a08abc7cd
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 892649 - Make sure elastic is never played when screen reader is enabled.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "77058600c39f678e5527cce73c9799105eeea5a9", 
+    "revision": "686f7e5027bdb74fb70bfc31bfadbe7fe317397c", 
     "repo_path": "/integration/gaia-central"
 }