Change something in _read_packets

I've some trouble to connect to socket.io server 2.1.1
I've made this change, and now everything works well.

socketIO_client/parsers.py

@@ -121,20 +121,17 @@ def _make_packet_prefix(packet):
 
 
 def _read_packet_length(content, content_index):
-    while get_byte(content, content_index) != 0:
-        content_index += 1
-    content_index += 1
     packet_length_string = ''
     byte = get_byte(content, content_index)
-    while byte != 255:
-        packet_length_string += str(byte)
+    while byte != 58: # ':'
+        packet_length_string += chr(byte)
         content_index += 1
         byte = get_byte(content, content_index)
     return content_index, int(packet_length_string)
 
 
 def _read_packet_text(content, content_index, packet_length):
-    while get_byte(content, content_index) == 255:
+    while get_byte(content, content_index) == 58: # ':'
         content_index += 1
     packet_text = content[content_index:content_index + packet_length]
     return content_index + packet_length, packet_text