Bumping gaia.json for 6 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/12379f829ad1
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #11247 from jmcanterafonseca/fb_link_broken

Bug 899503 - FB Link is broken after landing bug 895824

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https://hg.mozilla.org/integration/gaia-central/rev/589c5e9d560c
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 899503 - FB Link is broken after landing bug 895824

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https://hg.mozilla.org/integration/gaia-central/rev/fe2329f31cf3
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #11260 from cctuan/899422

Bug 899422 - [System][HD] lack of image assets

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https://hg.mozilla.org/integration/gaia-central/rev/4acc89b1bb75
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 899422 - [System][HD] lack of image assets

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https://hg.mozilla.org/integration/gaia-central/rev/8420b76828bb
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #11248 from jmcanterafonseca/fix_fb_passive_mode

Bug 899525 - In passive mode merge do not match existing FB Contacts

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https://hg.mozilla.org/integration/gaia-central/rev/02a817b06f5e
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 899525 - In passive mode merge do not match existing FB Contacts

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "af7ef38d9a648e76acc081eaa13dcd82459e979f", 
+    "revision": "12379f829ad18e0562c527e685e376ffc4c48994", 
     "repo_path": "/integration/gaia-central"
 }