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

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https://hg.mozilla.org/integration/gaia-central/rev/6fbc3880dac7
Author: Trif Andrei-Alin <trifandreialin@gmail.com>
Desc: Merge pull request #13474 from teodosia/sms-contact-travis

Bug 935587 - test_sms_add_contact.py - Adjust assertion and enable test for Travis

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https://hg.mozilla.org/integration/gaia-central/rev/57238f6bfbe1
Author: Teodosia Pop <teodosia.pop@gmail.com>
Desc: Bug 935587 - test_sms_add_contact.py - Adjust assertion and enable test for Travis

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "0c245e7915992520bcf0fd0644957841df0d15c8", 
+    "revision": "6fbc3880dac71e0a819cb0449a16134a010808f4", 
     "repo_path": "/integration/gaia-central"
 }