[string.replace] Add missing space (cplusplus#8170)

Author: Rageking8

source/strings.tex

@@ -4105,7 +4105,7 @@
 \begin{itemize}
 \item \tcode{out_of_range} if \tcode{pos1 > size()},
 \item \tcode{length_error} if the length of the resulting string
-would exceed\tcode{max_size()}, or
+would exceed \tcode{max_size()}, or
 \item any exceptions thrown by \tcode{allocator_traits<Allocator>::allocate.}
 \end{itemize}
 \end{itemdescr}