[docs] Fixed parameter to UnityToGymWrapper on line 34 and 37 (#4392)

Author: armando-fandango

Diff for: gym-unity/README.md

@@ -31,10 +31,10 @@ from the root of the project repository use:
 ```python
 from gym_unity.envs import UnityToGymWrapper
 
-env = UnityToGymWrapper(unity_environment, uint8_visual, flatten_branched, allow_multiple_obs)
+env = UnityToGymWrapper(unity_env, uint8_visual, flatten_branched, allow_multiple_obs)
 ```
 
-- `unity_environment` refers to the Unity environment to be wrapped.
+- `unity_env` refers to the Unity environment to be wrapped.
 
 - `uint8_visual` refers to whether to output visual observations as `uint8`
   values (0-255). Many common Gym environments (e.g. Atari) do this. By default