docs: Remove version from compose (#496)

compose.yml

@@ -1,4 +1,3 @@
-version: "3"
 services:
   windows:
     image: dockurr/windows

readme.md

@@ -28,7 +28,6 @@ Windows in a Docker container.
 Via Docker Compose:
 
 ```yaml
-version: "3"
 services:
   windows:
     image: dockurr/windows