Update cowlib to 0.5.1 to fix multipart issues

Makefile

@@ -11,7 +11,7 @@ PLT_APPS = crypto public_key ssl
 # Dependencies.
 
 DEPS = cowlib ranch
-dep_cowlib = pkg://cowlib 0.5.0
+dep_cowlib = pkg://cowlib 0.5.1
 dep_ranch = pkg://ranch 0.9.0
 
 TEST_DEPS = ct_helper gun

rebar.config

@@ -1,4 +1,4 @@
 {deps, [
-	{cowlib, ".*", {git, "git://github.com/extend/cowlib.git", "0.5.0"}},
+	{cowlib, ".*", {git, "git://github.com/extend/cowlib.git", "0.5.1"}},
 	{ranch, ".*", {git, "git://github.com/extend/ranch.git", "0.9.0"}}
 ]}.