WIF not returned

WIF is not properly returned.
```
from libcrypto import Wallet
wallet=Wallet('L4ZQks37JHUadEqaj2nGB1eaZFcsRZwZGQ7WVYuQiztzg4pqopU6')
wallet.private_key.to_wif()
```
gives:
```
libcrypto.formats.InvalidFormatError: Unsupported network: t
```

No network was given and bitcoin should be the default one.

Compressed WIF should be returned.

Seems like the problem may be in keys.py around line 64.