Update the "parameter name _..." error

Author: eernstg

specification/dartLangSpec.tex

@@ -2535,7 +2535,7 @@ \subsubsection{Optional Formals and Named Formals}
 if the static type of $d$ is not assignable to the declared type of $p$.
 
 \LMHash{}%
-It is a \Error{compile-time error} if the name of a named optional parameter
+It is a \Error{compile-time error} if the name of a named parameter
 begins with an `_' character.
 
 \rationale{%