Fix weird naming of variable

vim/neosnippets/go.snip

@@ -1,8 +1,8 @@
 snippet     middleware
 options     head
-    func ${1}(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
+    func ${1}(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
         ${2}
-        next(rw, r
+        next(w, r
     }
 
 snippet     handler