style fix

src/core/ngx_slab.c

diff --git a/src/core/ngx_slab.c b/src/core/ngx_slab.c
index b187026..233544b 100644
--- a/src/core/ngx_slab.c
+++ b/src/core/ngx_slab.c
@@ -685,7 +685,7 @@
     }
 
     ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, NGX_ENOMEM,
-                      "ngx_slab_alloc(): failed");
+                  "ngx_slab_alloc(): failed");
 
     return NULL;
 }