[dcl.dcl] Add missing \terminal to alias-declaration grammar.

Author: zygoloid

source/declarations.tex

@@ -44,7 +44,7 @@
 
 \begin{bnf}
 \nontermdef{alias-declaration}\br
-    \terminal{using} identifier attribute-specifier-seq\opt = type-id \terminal{;}
+    \terminal{using} identifier attribute-specifier-seq\opt \terminal{=} type-id \terminal{;}
 \end{bnf}
 
 \begin{bnf}