fix: control nginx docs typo (#597)

Admin Guide: fix typo

Author: QSmally

content/nginx/admin-guide/basic-functionality/runtime-control.md

@@ -32,7 +32,7 @@ where `<SIGNAL>` can be one of the following:
 - `quit` – Shut down gracefully (the `SIGQUIT` signal)
 - `reload` – Reload the configuration file (the `SIGHUP` signal)
 - `reopen` – Reopen log files (the `SIGUSR1` signal)
-- `stop` – Shut down immediately (or fast shutdown, the `SIGTERM` singal)
+- `stop` – Shut down immediately (or fast shutdown, the `SIGTERM` signal)
 
 The `kill` utility can also be used to send a signal directly to the master process. The process ID of the master process is written, by default, to the **nginx.pid** file, which is located in the **/usr/local/nginx/logs** or **/var/run** directory.