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

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https://hg.mozilla.org/integration/gaia-central/rev/84b895ff4787
Author: GaryChen,PYChen <mmm198219@gmail.com>
Desc: Merge pull request #18974 from mpizza/bug_979785_overwrite_settings_by_device_type

Bug 979785 - [GAIA][BUILD SYSTEM] Overwrite common-setting.json by GAIA_DEVICE_TYPE in build/settings.js. r=yurenju.

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https://hg.mozilla.org/integration/gaia-central/rev/2477ea0caadb
Author: mpizza <mmm198219@gmail.com>
Desc: Bug 979785 - [GAIA][BUILD SYSTEM] Overwrite common-setting.json by GAIA_DEVICE_TYPE in build/settings.js

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "d37aa6da234abefd5227511661ec6a365c1cfb84", 
+    "revision": "84b895ff478727d2924096da06ddcb2994488309", 
     "repo_path": "/integration/gaia-central"
 }