[expr.new] Add missing space (#1435)

Author: jensmaurer

source/expressions.tex

@@ -3120,7 +3120,7 @@
 expression~(\ref{expr.const}) of type \tcode{std\colcol{}size_t} and
 shall evaluate to a strictly positive value.
 \indextext{\idxcode{new}}%
-The \grammarterm{expression} in a \grammarterm{noptr-new-declarator}is
+The \grammarterm{expression} in a \grammarterm{noptr-new-declarator} is
 implicitly converted to \tcode{std\colcol{}size_t}.
 \begin{example}
 Given the definition \tcode{int n = 42},