fix(nginx): don't try to restart nginx when nginx isn't a thing

no issue
- if no promises are added to the array during uninstall, it means nginx isn't installed and we don't actually need to restart it

Author: acburdine

extensions/nginx/index.js

@@ -227,6 +227,10 @@ class NginxExtension extends cli.Extension {
             );
         }
 
+        if (!promises.length) {
+            return Promise.resolve();
+        }
+
         return Promise.all(promises).then(() => this.restartNginx());
     }