update package version

.yamato/com.unity.ml-agents-pack.yml

   commands:
     - |
       python3 -m pip install unity-downloader-cli --index-url https://artifactory.prd.it.unity3d.com/artifactory/api/pypi/pypi/simple --upgrade
-      unity-downloader-cli -u 2018.4 -c editor --wait --fast
+      unity-downloader-cli -u 2019.4 -c editor --wait --fast
       ./.Editor/Unity -projectPath Project -batchMode -executeMethod Unity.MLAgents.SampleExporter.ExportCuratedSamples -logFile -
       npm install upm-ci-utils@stable -g --registry https://artifactory.prd.cds.internal.unity3d.com/artifactory/api/npm/upm-npm
       upm-ci project pack --project-path Project

.yamato/com.unity.ml-agents-test.yml

 test_editors:
-  - version: 2018.4
-    # 2018.4 doesn't support code-coverage
-    enableCodeCoverage: !!bool false
+  - version: 2019.4
+    enableCodeCoverage: !!bool true
-    enableNoDefaultPackages: !!bool false
-  - version: 2019.4
-    enableCodeCoverage: !!bool true
-    testProject: DevProject
     enableNoDefaultPackages: !!bool true
   - version: 2020.2
     enableCodeCoverage: !!bool true

.yamato/test_versions.metafile

 # For each "other" test, we only run it against a single version of the
 # editor to reduce the number of yamato jobs
 test_editors:
-  - version: 2018.4
-    extra_test: llapi
+  - version: 2020.3
+    extra_test: sensor
+# TODO change to 2021.1 soon
-    extra_test: sensor
+    extra_test: llapi

com.unity.ml-agents.extensions/Documentation~/com.unity.ml-agents.extensions.md

 
 ## Requirements
 
-This version of the Unity ML-Agents Extensions package is compatible with the
-following versions of the Unity Editor:
+This version of the Unity ML-Agents package is compatible with the following
+versions of the Unity Editor:
-- If using the `InputActuatorComponent`
-    - 2019.4 or later
-    - install the `com.unity.inputsystem` package version `1.1.0-preview.3` or later.
-- Else 2018.4 and later
+- 2019.4 and later
+
+If using the `InputActuatorComponent`
+- install the `com.unity.inputsystem` package version `1.1.0-preview.3` or later.
 
 ## Known Limitations
 - For the `InputActuatorComponent`

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

   "name": "com.unity.ml-agents.extensions",
   "displayName": "ML Agents Extensions",
   "version": "0.3.0-preview",
-  "unity": "2018.4",
+  "unity": "2019.4",
   "description": "A source-only package for new features based on ML-Agents",
   "dependencies": {
     "com.unity.ml-agents": "2.0.0-exp.1"

com.unity.ml-agents/Documentation~/com.unity.ml-agents.md

 This version of the Unity ML-Agents package is compatible with the following
 versions of the Unity Editor:
 
-- 2018.4 and later
+- 2019.4 and later
 
 ## Known Limitations
 

com.unity.ml-agents/package.json

   "name": "com.unity.ml-agents",
   "displayName": "ML Agents",
   "version": "2.0.0-exp.1",
-  "unity": "2018.4",
+  "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": {
     "com.unity.barracuda": "1.3.2-preview",

docs/Installation.md

 
 Consequently, to install and use the ML-Agents Toolkit you will need to:
 
-- Install Unity (2018.4 or later)
+- Install Unity (2019.4 or later)
 - Install Python (3.6.1 or higher)
 - Clone this repository (Optional)
   - __Note:__ If you do not clone the repository, then you will not be
 - Install the `com.unity.ml-agents.extensions` Unity package (Optional)
 - Install the `mlagents` Python package
 
-### Install **Unity 2018.4** or Later
+### Install **Unity 2019.4** or Later
 
 [Download](https://unity3d.com/get-unity/download) and install Unity. We
 strongly recommend that you install Unity through the Unity Hub as it will

docs/Migrating.md

 
 # Migrating
 ## Migrating the package to version 2.0
+- The official version of Unity ML-Agents supports is now 2019.4 LTS. If you run
+  into issues, please consider deleting your project's Library folder and reponening your
+  project.
 - If you used any of the APIs that were deprecated before version 2.0, you need to use their replacement. These deprecated APIs have been removed. See the migration steps bellow for specific API replacements.
 ### IDiscreteActionMask changes
 - The interface for disabling specific discrete actions has changed. `IDiscreteActionMask.WriteMask()` was removed,