[namespace.udecl] Remove stray newline in grammar production (#1026)

Fixes #482.

Author: jensmaurer

source/declarations.tex

@@ -2674,7 +2674,7 @@
 
 \begin{bnf}
 \nontermdef{using-declaration}\br
-    \terminal{using typename\opt} nested-name-specifier unqualified-id \terminal{;}\br
+    \terminal{using typename\opt} nested-name-specifier unqualified-id \terminal{;}
 \end{bnf}
 
 The set of declarations introduced by the \grammarterm{using-declaration} is found by