Fix typo in nginx sample config

nginx/conf/nginx.conf.example

@@ -50,7 +50,7 @@ http {
         proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
         proxy_set_header    X-Forwarded-Proto   $scheme;
         proxy_set_header    Upgrade             $http_upgrade;
-        proxy_set-header    Connection          $connection_upgrade;
+        proxy_set_header    Connection          $connection_upgrade;
         proxy_read_timeout 300;