Raspberry python3.7: light.py fails to execute at `struct`

As is in python3.7, the example in the readme fails to run as: 

```File "/usr/local/lib/python3.7/dist-packages/lantern/light.py", line 62, in _send_packet
    packet = struct.pack(">BBBBBB",
NameError: name 'struct' is not defined 
```


adding `import struct` in `light.py` solves the error, and the example runs successfully as sudo.