add build-in module dependencies (#4384)

* add build-in module dependencies

* changelog

com.unity.ml-agents/CHANGELOG.md

 
 ### Minor Changes
 #### com.unity.ml-agents (C#)
-#### ml-agents / ml-agents-envs / gym-unity (Python)
-
-### Bug Fixes
-#### com.unity.ml-agents (C#)
-#### ml-agents / ml-agents-envs / gym-unity (Python)
-
-## [1.3.0-preview] - 2020-08-12
-
-### Major Changes
-#### com.unity.ml-agents (C#)
-#### ml-agents / ml-agents-envs / gym-unity (Python)
-
-### Minor Changes
-#### com.unity.ml-agents (C#)
 - Update Barracuda to 1.0.2.
 - Enabled C# formatting using `dotnet-format`.
 #### ml-agents / ml-agents-envs / gym-unity (Python)
+- The package dependencies were updated to include the built-in packages that are used also. (#4384)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 
 ## [1.3.0-preview] - 2020-08-12

com.unity.ml-agents/package.json

   "unity": "2018.4",
   "description": "Use state-of-the-art machine learning to create intelligent character behaviors in any Unity environment (games, robotics, film, etc.).",
   "dependencies": {
-    "com.unity.barracuda": "1.0.2"
+    "com.unity.barracuda": "1.0.2",
+    "com.unity.modules.imageconversion": "1.0.0",
+    "com.unity.modules.jsonserialize": "1.0.0",
+    "com.unity.modules.physics": "1.0.0",
+    "com.unity.modules.physics2d": "1.0.0"
   }
 }