Added version flag to manifest.json

Author: jellespijker

custom_components/ultimaker/manifest.json

@@ -5,5 +5,6 @@
   "issue_tracker": "https://github.com/jellespijker/home-assistant-ultimaker/issues",
   "dependencies": [],
   "codeowners": ["@jellespijker"],
-  "requirements": []
-}
+  "requirements": [],
+  "version": "2021.1.0"
+}