[keras/layers/preprocessing/hashing.py] Use backticks for defaults in…

… docstrings

keras/layers/preprocessing/hashing.py

@@ -109,12 +109,12 @@ class Hashing(base_layer.Layer):
  bin, so the effective number of bins is `(num_bins - 1)` if `mask_value`
  is set.
  mask_value: A value that represents masked inputs, which are mapped to
- index 0. None means no mask term will be added and the
+ index 0. `None` means no mask term will be added and the
  hashing will start at index 0. Defaults to `None`.
  salt: A single unsigned integer or None.
  If passed, the hash function used will be SipHash64, with these values
  used as an additional input (known as a "salt" in cryptography).
- These should be non-zero. If None, uses the FarmHash64 hash function.
+ These should be non-zero. If `None`, uses the FarmHash64 hash function.
  It also supports tuple/list of 2 unsigned integer numbers, see
  reference paper for details. Defaults to `None`.
  output_mode: Specification for the output of the layer. Values can bes