Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/f31df80b4f3f
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #21879 from gaye/bump-chai-to-1.9.1

Upgrade chai to 1.9.1 to downstream assert.notInclude

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https://hg.mozilla.org/integration/gaia-central/rev/0af98e7f74f1
Author: gaye <gaye@mozilla.com>
Desc: Upgrade chai to 1.9.1 to downstream assert.notInclude

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https://hg.mozilla.org/integration/gaia-central/rev/967625a4fa81
Author: James Graham <james@hoppipolla.co.uk>
Desc: Bug 1040045 - Move code for waiting for the homescreen in gaiatest into its own method. r=dhunt

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "b2b836ff2b51c9b13b9148fbd0bd974707c1cd5a", 
+    "revision": "f31df80b4f3f69b403da684cb01b415d046e884e", 
     "repo_path": "/integration/gaia-central"
 }