Changing minimum version to 2020.3

com.unity.perception/package.json

   "description": "Tools for generating large-scale data sets for perception-based machine learning training and validation",
   "displayName": "Perception",
   "name": "com.unity.perception",
-  "unity": "2019.4",
+  "unity": "2020.3",
   "version": "0.8.0-preview.3",
   "samples": [
     {