add version command

lib/cmd.js

@@ -17,6 +17,7 @@ class Cmd {
     this.simulator();
     this.test();
     this.upload();
+    this.versionCmd();
     this.otherCommands();
 
     //If no arguments are passed display help by default
@@ -156,6 +157,16 @@ class Cmd {
       });
   }
 
+  versionCmd() {
+    program
+    .command('version')
+    .description('output the version number')
+    .action(function () {
+      console.log(embark.version);
+      process.exit(0);
+    });
+  }
+
   otherCommands() {
     program
       .action(function (env) {