message: Update MAC primitive variable name to avoid naming conflict with imported module.
  Should make it easier to cut-and-paste MAC Python example.
diff: @@ -282,13 +282,13 @@ mac.register()
  keyset_handle = tink.new_keyset_handle(mac.mac_key_templates.HMAC_SHA256_128BITTAG)
  # 2. Get the primitive.
  -mac = keyset_handle.primitive(mac.Mac)
  +mac_primitive = keyset_handle.primitive(mac.Mac)
  # 3. Use the primitive to compute a tag,
  -tag = mac.compute_mac(data)
  +tag = mac_primitive.compute_mac(data)
  # ... or to verify a tag.
  -mac.verify_mac(tag, data)
  +mac_primitive.verify_mac(tag, data)
  ```
  ### Hybrid Encryption
  