[library.general] Fix typo.

Fixes: cplusplus#538

source/lib-intro.tex

@@ -54,7 +54,7 @@
 storage management~(\ref{basic.stc.dynamic}), and components used
 as infrastructure
 in \Cpp programs,
-such as a tuples, function wrappers, and time facilities.
+such as tuples, function wrappers, and time facilities.
 
 \pnum
 The strings library (Clause~\ref{strings}) provides support for manipulating text represented