docs: PreConditionerType docstring

pytorch_optimizer/optimizer/shampoo_utils.py

@@ -182,7 +182,7 @@ class PreConditionerType(IntEnum):
  r"""Type of PreConditioner.
 
  In default (ALL), computes pre-conditioner for each dim.
- INPUT is one-sided Shampoo, in this cases only on input dim.
+ INPUT is one-sided Shampoo, in this case only on input dim.
  Assumes last dim is always the output dim and everything else input dim.
  """