Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/5b4a1d76f824
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #21550 from AdFad666/master

Bug 1036553 Fix cropped software home button

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https://hg.mozilla.org/integration/gaia-central/rev/c409e7af7e55
Author: Adam Farden <adam@farden.cz>
Desc: Bug 1036553 Fix cropped software home button

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "6b043e9d825f4b6e1017648633be5f0be15f8330", 
+    "revision": "5b4a1d76f824bdde90a5c3be6bd5f986b0646af1", 
     "repo_path": "/integration/gaia-central"
 }