Update rebar.config

rebar.config

@@ -1,4 +1,4 @@
 {deps, [
-	{cowlib, ".*", {git, "git://github.com/extend/cowlib.git", "0.5.1"}},
+	{cowlib, ".*", {git, "git://github.com/extend/cowlib.git", "0.6.0"}},
 	{ranch, ".*", {git, "git://github.com/extend/ranch.git", "0.9.0"}}
 ]}.