Update error message for missing connector

lib/datasource.js

@@ -234,7 +234,7 @@ DataSource._resolveConnector = function (name, loader) {
   var error = null;
   if (!connector) {
     error = util.format('\nWARNING: LoopBack connector "%s" is not installed ' +
-      'as any of the following modules:\n\n %s\n\nTo fix, run:\n\n    npm install %s\n',
+      'as any of the following modules:\n\n %s\n\nTo fix, run:\n\n    npm install %s --save\n',
       name, names.join('\n'), names[names.length - 1]);
   }
   return {