Exit on install if node is not installed.

bin/installOnWindows.bat

@@ -3,6 +3,10 @@
 :: change directory to etherpad-lite root
 cd /D "%~dp0\.."
 
+:: Is node installed?
+cmd /C node -e "" || ( echo "Please install node.js ( http://nodejs.org )" && exit /B 1 )
+
+echo _
 echo Checking node version...
 set check_version="if(['6','8'].indexOf(process.version.split('.')[1].toString()) === -1) { console.log('You are running a wrong version of Node. Etherpad Lite requires v0.6.x or v0.8.x'); process.exit(1) }"
 cmd /C node -e %check_version% || exit /B 1