Let buck ignore the .git folder

According to [1] buck makes no assumption about source code versioning
systems which means that it will also scan the .git folder for the file
system monitoring (buckd) and when searching for the BUCK files.

[1] http://facebook.github.io/buck/concept/buckconfig.html

Change-Id: Ic9248326232684f8b85a951f5b01b542127a080a

.buckconfig

@@ -15,3 +15,6 @@
 
 [java]
   src_roots = java, resources
+
+[project]
+  ignore = .git