[char.traits.require]: Use "class template" instead of "struct template".

Author: FrankHB

source/strings.tex

@@ -194,7 +194,7 @@
 \end{libreqtab4d}
 
 \pnum
-The struct template
+The class template
 
 \indexlibrary{\idxcode{char_traits}}%
 \begin{codeblock}