Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/4880b2c2db28
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1155907 - merge pull request #29674 from sfoster:task-manager-hide-events-bug-1155907 to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/378c08cc5941
Author: Sam Foster <sfoster@mozilla.com>
Desc: Bug 1155907 - Remove listeners immediately in exitToApp r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/609b70522a62
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1152969 - merge pull request #29689 from Cwiiis:bug1152969-can-save-empty-bookmark-name to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/993dafa46c3b
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 1152969 - Fix being able to save empty bookmark names. r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/16cd2416bbbd
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1156571 - merge pull request #29671 from hfiguiere:bug1156571-bidi-fixes to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/d039be2ccf05
Author: Hubert Figuière <hub@figuiere.net>
Desc: Bug 1156571 - Fix BiDi display of song titles.

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "0c5e2ee1173f3c53379ef3cd10de714836258fe8", 
+        "git_revision": "dd80f9fed5f719330c0abd556cfc32bf9eea2b31", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "910522407a1dd40c9302f2e342f8cf1d4828fc3b", 
+    "revision": "4880b2c2db28a6bcdf407e6651b2474ddfd5f095", 
     "repo_path": "integration/gaia-central"
 }