Lib throws for the call `net_peerCount`

In my project, I use `testrpc` as the environment for my unit tests.
And `ehjsonrpc` throws for the call `net_peerCount` with this:
```
File "/../src/venv/lib/python3.5/site-packages/ethjsonrpc/client.py", line 175, in net_peerCount
return hex_to_dec(self._call('net_peerCount'))
File "/../src/venv/lib/python3.5/site-packages/ethjsonrpc/utils.py", line 10, in hex_to_dec
return int(x, 16)
TypeError: int() can't convert non-string with explicit base
```

I found a quick fix
https://github.com/ConsenSys/ethjsonrpc/blob/master/ethjsonrpc/utils.py#L8
```
def hex_to_dec(x):
if type(x) is int:
return x
return int(x, 16)
```