I tried to `pms.adsb.surface_velocity()` as per README with a typecode 19 msg and got an error:
```python
>>> import pyModeS as pms
>>> msg = '8d484966990076b9e0762d5ff92c'
>>> pms.adsb.typecode(msg)
19
>>> pms.adsb.surface_velocity(msg)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Users\spi\AppData\Roaming\Python\Python27\site-packages\pyModeS\decoder\bds\bds06.py", line 162, in surface_velocity
raise RuntimeError("%s: Not a surface message, expecting 5<TC<8" % msg)
RuntimeError: 8d484966990076b9e0762d5ff92c: Not a surface message, expecting 5<TC<8
```
so I propose this fix.
I used pyModeS 2.2
