SSL: fixed typo in the error message.

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 2c4e114..07646b6 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -3128,7 +3128,7 @@
 {
     if (paths) {
         ngx_log_error(NGX_LOG_WARN, ssl->log, 0,
-                      "\"ssl_session_ticket_keys\" ignored, not supported");
+                      "\"ssl_session_ticket_key\" ignored, not supported");
     }
 
     return NGX_OK;