Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/bb39865b82c1
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #27870 from huchengtw-moz/bug-1125780-v2

Bug 1125780 - [Stingray] Use event name to check if we need to invoke _c..., r=lchang

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https://hg.mozilla.org/integration/gaia-central/rev/2b9e8fa7f36c
Author: John Hu <johu@mozilla.com>
Desc: Bug 1125780 - [Stingray] Use event name to check if we need to invoke _closing handler

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https://hg.mozilla.org/integration/gaia-central/rev/b1c3d2d469c9
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #27805 from sean2449/Bug_1122432

Bug 1122432 - [Stingray] UI-Transition - Banner, r=johnhu

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https://hg.mozilla.org/integration/gaia-central/rev/075a3e6b24a6
Author: Sung Chiu <suchiu@mozilla.com>
Desc: Bug 1122432 [Stingray] UI-Transition - Banner

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "97f3b4d11a92bdcaf79edd8ff55e690bd446bac7", 
+        "git_revision": "1b91ddf0d79520e8e64c0eede23dbbeed5e172e2", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "97c2d9a539684edc11c5d9b0fd6862bddc9d8e34", 
+    "revision": "bb39865b82c125120fe6cbc5e589390a0d34f145", 
     "repo_path": "integration/gaia-central"
 }