add webm ext (2/3)

appveyor-macos.yml

@@ -28,6 +28,8 @@ install:
   - haxelib git faxe https://github.com/uhrobots/faxe
   - haxelib git polymod https://github.com/larsiusprime/polymod.git
   - haxelib git discord_rpc https://github.com/Aidan63/linc_discord-rpc
+  - haxelib git extension-webm https://github.com/KadeDev/extension-webm
+  - lime rebuild extension-webm macos
   - haxelib install linc_luajit
   - haxelib list
   - cd /Users/appveyor/projects/kade-engine-macos