Update batchnorm docstrings

Add missing full stops, and added blank line for increased clarity on rendered documentation.

Author: ronrest

torch/nn/modules/batchnorm.py

@@ -60,7 +60,8 @@ class BatchNorm1d(_BatchNorm):
  of size N (where N is the input size).
 
  During training, this layer keeps a running estimate of its computed mean
- and variance. The running sum is kept with a default momentum of 0.1
+ and variance. The running sum is kept with a default momentum of 0.1.
+ 
  During evaluation, this running mean/variance is used for normalization.
 
  Args:
@@ -100,7 +101,8 @@ class BatchNorm2d(_BatchNorm):
  of size N (where N is the input size).
 
  During training, this layer keeps a running estimate of its computed mean
- and variance. The running sum is kept with a default momentum of 0.1
+ and variance. The running sum is kept with a default momentum of 0.1.
+ 
  During evaluation, this running mean/variance is used for normalization.
 
  Args:
@@ -140,7 +142,8 @@ class BatchNorm3d(_BatchNorm):
  of size N (where N is the input size).
 
  During training, this layer keeps a running estimate of its computed mean
- and variance. The running sum is kept with a default momentum of 0.1
+ and variance. The running sum is kept with a default momentum of 0.1.
+ 
  During evaluation, this running mean/variance is used for normalization.
 
  Args: