Update version to 2.0-alpha.3

Author: AlexxIT

custom_components/xiaomi_gateway3/manifest.json

@@ -7,6 +7,6 @@
   "codeowners": ["@AlexxIT"],
   "dependencies": ["http"],
   "requirements": ["zigpy>=0.33.0"],
-  "version": "2.0a2",
+  "version": "2.0a3",
   "iot_class": "local_push"
 }