warnings module need be import in python3

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.

We changed it, thanks for pointing this out!

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