warnings module need be import in python3

[Ming]

TTUR/fid.py

Lines 140 to 142 in dc4e5b5

 if not np.isfinite(covmean).all(): 
     msg = "fid calculation produces singular product; adding %s to diagonal of cov estimates" % eps 
     warnings.warn(msg) 

The warnings module need be import explicitly. I got a error that the name is not defined by Python3.6, although it is usually not happened because the branch is often skipped.

[Martin Heusel]

We changed it, thanks for pointing this out!