#7 Bug fix with npm executable

src/Handler.php

@@ -358,7 +358,9 @@ class Handler
     if ($update) {
       $this->npm('update');
     }
-    $this->npm('install');
+    else {
+      $this->npm('install');
+    }
 
     // Handle Bower if not installed globally
     if (!$this->getOption('bower_assets')['global']) {