I'm getting syntax error  trying loading nlp (webdataset  import)
from nemo.collections import nlp as nemo_nlp gives me an error 


```
File "/usr/local/lib/python3.7/dist-packages/webdataset/cache.py", line 43
    while data := stream.read(chunk_size):
                ^
SyntaxError: invalid syntax
```

that looks to originate in webdataset  import. 
The webdataset version 0.2.4
and the last version of Nemo. 

Anyone can help? 