(case 1255312) Conditionally use different namespace for ScriptedImporters (#4188)

* (case 1255312) Conditionally use different namespace for ScriptedImporters.

* Add semi-colon.

* Update barracuda dependency.

* Update changelog.

* Fix PR number.

com.unity.ml-agents/CHANGELOG.md

 #### com.unity.ml-agents (C#)
 - `SideChannelsManager` was renamed to `SideChannelManager`. The old name is still supported, but deprecated. (#4137)
 - `RayPerceptionSensor.Perceive()` now additionally store the GameObject that was hit by the ray. (#4111)
-- The Barracuda dependency was upgraded to 1.0.0 (#4118)
+- The Barracuda dependency was upgraded to 1.0.1 (#4188)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 - Added new Google Colab notebooks to show how to use `UnityEnvironment'. (#4117)
 

com.unity.ml-agents/Editor/DemonstrationImporter.cs

 using Unity.MLAgents.CommunicatorObjects;
 using UnityEditor;
 using UnityEngine;
+#if UNITY_2020_2_OR_NEWER
+using UnityEditor.AssetImporters;
+#else
+#endif
 using Unity.MLAgents.Demonstrations;
 
 namespace Unity.MLAgents.Editor

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": "1.0.0"
+    "com.unity.barracuda": "1.0.1"
   }
 }