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

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https://hg.mozilla.org/integration/gaia-central/rev/57708271ce66
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1142381 - merge pull request #28824 from KevinGrandon:bug_1142381_symlinked_apps_fix to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/d68b6fe85898
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1142381 - [Build] Guard symlinked apps

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "e358c1ba5782694eeb217436abbc00c310307859", 
+        "git_revision": "f73a7dc52b662edd3d4490ca2d8300eff4838090", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "6ecc772fc32c57aeb56d7f9977afb4eabf1c73ba", 
+    "revision": "57708271ce66fbfb271237b2e7ba053d89b2ff0e", 
     "repo_path": "integration/gaia-central"
 }