message: Fix typo in doc
  Summary: poplar->paper
  Test Plan: none
  Reviewers: jakeh
diff: @@ -32,7 +32,7 @@ Group normalization
  Group normalization is an alternative to batch normalization, and produces
  smaller and more optimized graphs.
  -The original poplar on group normalization:
  +The original paper on group normalization:
  `"Group Normalization", Yuxin Wu, Kaiming He <https://arxiv.org/abs/1803.08494>`_.
  See :py:func:`tensorflow.contrib.ipu.group_norm`.
  