Fix syntax error in connectionmanager.py

There's an erroneous double '::' that resulted in:

```
Traceback (most recent call last):
  File "yowsup-cli", line 33, in <module>
    from Examples.CmdClient import WhatsappCmdClient
  File "/Users/anant/Code/whatsapp/yowsup/src/Examples/CmdClient.py", line 21, in <module>
    from Yowsup.connectionmanager import YowsupConnectionManager
  File "/Users/anant/Code/whatsapp/yowsup/src/Yowsup/connectionmanager.py", line 1326
    if vcardName and not sys.version_info < (3, 0)::
                                                   ^
SyntaxError: invalid syntax
```