Fix qmk_install.sh on Windows dropping to command prompt (#6488)

util/win_shared_install.sh

@@ -34,7 +34,7 @@ function install_drivers {
     pushd "$download_dir"
     cp -f "$dir/drivers.txt" .
     echo 
-    cmd.exe /c "qmk_driver_installer.exe $1 $2 drivers.txt"
+    cmd.exe //c "qmk_driver_installer.exe $1 $2 drivers.txt"
     popd > /dev/null
 }