fixed nccl init

pytorch_lightning/utils/plotting.py

@@ -1,4 +1,3 @@
-from matplotlib import pyplot as plt
 import numpy as np
 np.seterr(divide='ignore', invalid='ignore')
 
@@ -13,6 +12,7 @@ def plot_confusion_matrix(cm,
     This function prints and plots the confusion matrix.
     Normalization can be applied by setting `normalize=True`.
     """
+    from matplotlib import pyplot as plt
     if normalize:
         cm = cm.astype('float') / cm.sum(axis=1)[:, np.newaxis]
         print("Normalized confusion matrix")