add hostname to error message invalid hostname

lib/request_urls.js

@@ -81,7 +81,7 @@ function request_urls(config, urls, callback) {
         console.error( err );
         //Check if hostname is valid. Abort execution if not
         if( err.code === 'ENOTFOUND' ) {
-          throw new Error( 'Invalid hostname, exiting' );
+          throw new Error( 'Invalid hostname: "'+ err.hostname + '". Stopping execution.' );
         }
         urls.push(url);
       }