add twitter for Buenos Aires chapter

Author: a0viedo

chapters/buenosaires.json

@@ -5,6 +5,6 @@
   "region": "Latin America",
   "organizers": ["a0viedo"],
   "website": "http://nodeschool.io/buenosaires",
-  "twitter": "",
+  "twitter": "nodeschoolba",
   "repo": "http://github.com/nodeschool/buenosaires"
-}
+}