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

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https://hg.mozilla.org/integration/gaia-central/rev/8ff42fad2e15
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #13367 from stupchiy/issue_933075

Bug 933709 - Write test for geolocation prompt

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https://hg.mozilla.org/integration/gaia-central/rev/1f2265e62705
Author: Sergey Tupchiy <sergey.tupchiy@optile.de>
Desc: Bug 933709 - Write test for geolocation prompt

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "7b595379c0f98844aa2e4d75c8c54d90df94c9a2", 
+    "revision": "8ff42fad2e152e5703d3268e1c5454bcdc7fb961", 
     "repo_path": "/integration/gaia-central"
 }