message: Update ragged_array_ops.py
  typo
diff: @@ -448,7 +448,7 @@ def boolean_mask(data, mask, keepdims=False, name=None):
  # Get static rank of mask.
  if mask.shape.ndims is None:
  - raise ValueError('mask.shape.ndims must be kown statically.')
  + raise ValueError('mask.shape.ndims must be known statically.')
  elif mask.shape.ndims == 0:
  raise ValueError('mask cannot be scalar.')
  