fix: Update nginx server_name variable syntax

nginx.conf

@@ -1,6 +1,6 @@
 server {
     listen 80;
-    server_name ${SERVER_IP};
+    server_name $SERVER_IP;
 
     gzip on;
     gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;