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

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https://hg.mozilla.org/integration/gaia-central/rev/9a31ee47215f
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #24630 from julienw/1076169-fix-camera-tests

Bug 1076169 - [Camera] fix camera tests with a newer mocha (again) r=wil...

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https://hg.mozilla.org/integration/gaia-central/rev/812eaecf52e2
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1076169 - [Camera] fix camera tests with a newer mocha (again) r=wilsonpage

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https://hg.mozilla.org/integration/gaia-central/rev/f379765506ae
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #24855 from davidflanagan/bug1072075

Bug 1072075: don't allow system time changes to affect app usage timings r=marshall

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https://hg.mozilla.org/integration/gaia-central/rev/8e1e26d38a58
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 1072075: don't allow system time changes to affect app usage timings
(cherry picked from commit 83af4279c67b36c96b04ffec04ae428b69eec51d)

reference bug 1069863 in comments

fix broken unit tests

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "c98710d8aeb492eef503879c8542e90818a3839c", 
+    "revision": "9a31ee47215fa87eef704cc51c11f64510319fb0", 
     "repo_path": "/integration/gaia-central"
 }