Remove vis_encode_type from list of required (#3677)

com.unity.ml-agents/CHANGELOG.md

  - Format of console output has changed slightly and now matches the name of the model/summary directory. (#3630, #3616)
  - Raise the wall in CrawlerStatic scene to prevent Agent from falling off. (#3650)
  - Renamed 'Generalization' feature to 'Environment Parameter Randomization'.
+ - Fixed an issue where specifying `vis_encode_type` was required only for SAC. (#3677)
  - The way that UnityEnvironment decides the port was changed. If no port is specified, the behavior will depend on the `file_name` parameter. If it is `None`, 5004 (the editor port) will be used; otherwise 5005 (the base environment port) will be used.
 
 ## [0.15.0-preview] - 2020-03-18

ml-agents/mlagents/trainers/sac/trainer.py

             "memory_size",
             "model_path",
             "reward_signals",
-            "vis_encode_type",
         ]
 
         self._check_param_keys()