Prevent rm complaining when removing one artifaft

makefile

@@ -13,4 +13,4 @@ $(win-artifact-name): main.cpp
 	$(win-compiler) main.cpp -o $(win-artifact-name)
 
 clean:
-	rm $(linux-artifact-name) $(win-artifact-name)
+	rm -f $(linux-artifact-name) $(win-artifact-name)