Sort imports with isort.

This is the result of:

    $ isort --recursive examples templates transformers utils hubconf.py setup.py

examples/pplm/run_pplm.py

@@ -34,10 +34,11 @@ import torch.nn.functional as F
 from torch.autograd import Variable
 from tqdm import trange
 
+from pplm_classification_head import ClassificationHead
 from transformers import GPT2Tokenizer
 from transformers.file_utils import cached_path
 from transformers.modeling_gpt2 import GPT2LMHeadModel
-from pplm_classification_head import ClassificationHead
+
 
 PPLM_BOW = 1
 PPLM_DISCRIM = 2