Closes socket when receiving malformed messages from client. Node-stratum now passes 20k concurrent requests with apache benchmark test.

lib/stratum.js

@@ -170,8 +170,11 @@ var StratumClient = function(options){
                         messageJson = JSON.parse(message);
                     } catch(e) {
                         _this.emit('malformedMessage', message);
+                        socket.end();
+                        return;
                     }
-                    
+
+
                     if (messageJson) {
                         handleMessage(messageJson);
                     }