message: Update filter_ops.py
  currently for every mode value other than None - a 'NameError: name 'upper' is not defined' was thrown due to misuse of the 'upper' method
diff: @@ -22,7 +22,7 @@ import tensorflow as tf
  def pad(input, ksize, mode, constant_values):
  input = tf.convert_to_tensor(input)
  ksize = tf.convert_to_tensor(ksize)
  - mode = "CONSTANT" if mode is None else upper(mode)
  + mode = "CONSTANT" if mode is None else str.upper(mode)
  constant_values = (
  tf.zeros([], dtype=input.dtype)
  if constant_values is None
  