add error message for unsupported versions of node

bin/embark

@@ -1,4 +1,14 @@
 #!/usr/bin/env node
+
+try {
+  eval('let __nodeTest = 123;');
+} catch(e) {
+  if (e.name === 'SyntaxError') {
+    console.error("unsupported version of NodeJS. Make sure you are running nodejs 6.9.5 or above");
+    process.exit();
+  }
+}
+
 var Cmd = require('../lib/cmd');
 var cli = new Cmd();
 cli.process(process.argv);