Use %s for errors returned from configuration parsing handlers.

src/core/ngx_conf_file.c

diff --git a/src/core/ngx_conf_file.c b/src/core/ngx_conf_file.c
index e92cd33..6d1629e 100644
--- a/src/core/ngx_conf_file.c
+++ b/src/core/ngx_conf_file.c
@@ -310,7 +310,7 @@
                 goto failed;
             }
 
-            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, rv);
+            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "%s", rv);
 
             goto failed;
         }