[dcl.fct] Make bnf indentation in source match presentation. (#1362)

Author: Eelis

source/declarators.tex

@@ -1320,7 +1320,7 @@
 \indextext{declaration!function}%
 \begin{bnf}
 \nontermdef{parameter-declaration-clause}\br
-parameter-declaration-list\opt{} \terminal{...}\opt\br
+    parameter-declaration-list\opt{} \terminal{...}\opt\br
     parameter-declaration-list \terminal{, ...}
 \end{bnf}