Fix python3 support

Author: Arnau Orriols

lib/python-function.js

@@ -86,9 +86,12 @@ module.exports = function (RED) {
       code: `
 import os
 import json
+import sys
 
-channel = os.fdopen(3, "r+")
-
+if sys.version_info[0]<3:
+    channel = os.fdopen(3, "r+")
+else:
+    channel = os.fdopen(3, "r+b", buffering=0)
 
 class Msg(object):
     SEND = 'send'
@@ -136,7 +139,7 @@ class Node(object):
         self.send_to_node(msg)
 
     def send_to_node(self, msg):
-        self.__channel.write(msg.dumps())
+        self.__channel.write(msg.dumps().encode('utf-8'))
 
 
 def python_function(msg):