[forward.list] Replace misplaced comma with period (#7246)

Author: Quuxplusone

source/containers.tex

@@ -7011,7 +7011,7 @@
 A \tcode{forward_list} meets all of the requirements
 of a container\iref{container.reqmts},
 except that the \tcode{size()} member function is not provided and
-\tcode{operator==} has linear complexity,
+\tcode{operator==} has linear complexity.
 A \tcode{forward_list} also meets all of the requirements
 for an allocator-aware container\iref{container.alloc.reqmts}.
 In addition, a \tcode{forward_list}