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

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https://hg.mozilla.org/integration/gaia-central/rev/a5b8211be132
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #12065 from alivedise/bugzilla/914412/set-activity-caller-visibility-correctly

Bug 914412 - Set page visibility of activity opener if it's in-process correctly. r=timdream, a=koi+

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https://hg.mozilla.org/integration/gaia-central/rev/7b707c165f40
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 914412 - Set browser app's page visibility as an activity opener correctly.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "c8917f89f9f48c5bac22ae0605b674d3e0e79b01", 
+    "revision": "a5b8211be132f1997bba44873a80a62597867abb", 
     "repo_path": "/integration/gaia-central"
 }