Docs: Fix Typo

Author: HeikoSchlittermann

doc/doc-docbook/spec.xfpt

@@ -20848,7 +20848,7 @@ is forced to fail, no action is taken. Other expansion failures are treated as
 errors and cause the delivery to be deferred.
 
 Unlike most options, &%headers_remove%& can be specified multiple times
-for a router; all listed headers are removed.
+for a transport; all listed headers are removed.
 
 &*Warning*&: Because of the separate expansion of the list items,
 items that contain a list separator must have it doubled.