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

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https://hg.mozilla.org/integration/gaia-central/rev/b8dd552c61e7
Author: Ben Francis <ben@tola.me.uk>
Desc: Merge pull request #18762 from rnowm/1002501

Bug 1002501 - Regression: Incorrect background colour of disabled back/forward buttons r=benfrancis

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https://hg.mozilla.org/integration/gaia-central/rev/920075e6f426
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 1002501 - Regression: Incorrect background colour of disabled back/forward buttons

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "d327e9514a8b8e44ef9fd89c5d8d6d21b3853485", 
+    "revision": "b8dd552c61e7df04273319f9d591616dd23e50c1", 
     "repo_path": "/integration/gaia-central"
 }