fix counterparty-client NoneType error
fix counterparty-client NoneType error

fixes:

```
$ counterparty-client --help
Traceback (most recent call last):
  File "/bin/counterparty-client", line 9, in <module>
    load_entry_point('counterparty-cli==1.1.2', 'console_scripts', 'counterparty-client')()
  File "/usr/lib/python3.5/site-packages/counterpartycli/__init__.py", line 12, in client_main
    client.main()
  File "/usr/lib/python3.5/site-packages/counterpartycli/client.py", line 73, in main
    subparsers = parser.add_subparsers(dest='action', help='the action to be taken')
AttributeError: 'NoneType' object has no attribute 'add_subparsers'
```

CounterpartyXCP/counterparty-cli