Update package versions for main branch (#5413)

DevProject/Packages/packages-lock.json

       "depth": 0,
       "source": "local",
       "dependencies": {
-        "com.unity.ml-agents": "2.0.0-exp.1",
+        "com.unity.ml-agents": "2.1.0-exp.1",
         "com.unity.modules.physics": "1.0.0"
       }
     },

Project/Packages/packages-lock.json

       "depth": 0,
       "source": "local",
       "dependencies": {
-        "com.unity.ml-agents": "2.0.0-exp.1",
+        "com.unity.ml-agents": "2.1.0-exp.1",
         "com.unity.modules.physics": "1.0.0"
       }
     },

com.unity.ml-agents.extensions/package.json

 {
   "name": "com.unity.ml-agents.extensions",
   "displayName": "ML Agents Extensions",
-  "version": "0.4.0-preview",
+  "version": "0.5.0-preview",
-    "com.unity.ml-agents": "2.0.0-exp.1",
+    "com.unity.ml-agents": "2.1.0-exp.1",
     "com.unity.modules.physics": "1.0.0"
   }
 }

com.unity.ml-agents/Runtime/Academy.cs

         /// Unity package version of com.unity.ml-agents.
         /// This must match the version string in package.json and is checked in a unit test.
         /// </summary>
-        internal const string k_PackageVersion = "2.0.0-exp.1";
+        internal const string k_PackageVersion = "2.1.0-exp.1";
 
         const int k_EditorTrainingPort = 5004;
 

com.unity.ml-agents/package.json

 {
   "name": "com.unity.ml-agents",
   "displayName": "ML Agents",
-  "version": "2.0.0-exp.1",
+  "version": "2.1.0-exp.1",
   "unity": "2019.4",
   "description": "Use state-of-the-art machine learning to create intelligent character behaviors in any Unity environment (games, robotics, film, etc.).",
   "dependencies": {

gym-unity/gym_unity/__init__.py

 # Version of the library that will be used to upload to pypi
-__version__ = "0.27.0.dev0"
+__version__ = "0.28.0.dev0"
 
 # Git tag that will be checked to determine whether to trigger upload to pypi
 __release_tag__ = None

ml-agents-envs/mlagents_envs/__init__.py

 # Version of the library that will be used to upload to pypi
-__version__ = "0.27.0.dev0"
+__version__ = "0.28.0.dev0"
 
 # Git tag that will be checked to determine whether to trigger upload to pypi
 __release_tag__ = None

ml-agents/mlagents/trainers/__init__.py

 # Version of the library that will be used to upload to pypi
-__version__ = "0.27.0.dev0"
+__version__ = "0.28.0.dev0"
 
 # Git tag that will be checked to determine whether to trigger upload to pypi
 __release_tag__ = None