message: fixed typo in docstring
  `init_from_checkpoint` does not accept a set as `assignment_map`
diff: @@ -147,7 +147,7 @@ def init_from_checkpoint(ckpt_dir_or_file, assignment_map):
  partitioner=lambda shape, dtype: [5, 1])
  # Initialize all variables in `new_scope_1` from `old_scope_1`.
  - init_from_checkpoint('/tmp/model.ckpt', {'old_scope_1/', 'new_scope_1'})
  + init_from_checkpoint('/tmp/model.ckpt', {'old_scope_1/': 'new_scope_1'})
  # Use names to specify which variables to initialize from checkpoint.
  init_from_checkpoint('/tmp/model.ckpt',
  