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

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https://hg.mozilla.org/integration/gaia-central/rev/4b40bac5bfbc
Author: Evyatar Amitay <evyatron@gmail.com>
Desc: Merge pull request #10579 from EverythingMe/bugfix-helper-title

[Bug 886324] Fix helper's title not showing properly [r=crdlc]

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https://hg.mozilla.org/integration/gaia-central/rev/3eadd9354f5b
Author: Evyatar Amitay <evyatron@gmail.com>
Desc: [Bug 886324] Fix helper's title not showing properly [r=crdlc]

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "31681e1eff4809b139b7548df8f469aece0ea927", 
+    "revision": "4b40bac5bfbc3c786f1d1d33a3a6fa6f94fcbf95", 
     "repo_path": "/integration/gaia-central"
 }