dart: minor content fix

dart/content.md

@@ -29,7 +29,7 @@ RUN dart pub get
 COPY . .
 # Ensure packages are still up-to-date if anything has changed
 RUN dart pub get --offline
-RUN dart compile exe bin/server.dart -o /server
+RUN dart compile exe bin/server.dart -o bin/server
 
 # Build minimal serving image from AOT-compiled `/server` and required system
 # libraries and configuration files stored in `/runtime/` from the build stage.