doc: add missing s (Thanks Ludovic Stordeur for reporting it)

doc/chapters/advanced-examples.texi

@@ -66,7 +66,7 @@ struct starpu_codelet cl = @{
 @end smallexample
 @end cartouche
 
-Scheduler which are multi-implementation aware (only @code{dmda}, @code{heft}
+Schedulers which are multi-implementation aware (only @code{dmda}, @code{heft}
 and @code{pheft} for now) will use the performance models of all the
 implementations it was given, and pick the one that seems to be the fastest.