tour: fix grammatical error on Named Return Values page

Change-Id: Ide88384feaa257eab2df67912699f4c28240c859
Reviewed-on: https://go-review.googlesource.com/8667
Reviewed-by: Francesc Campoy Flores <campoy@golang.org>
diff --git a/content/basics.article b/content/basics.article
index 1f54048..710bd85 100644
--- a/content/basics.article
+++ b/content/basics.article
@@ -88,7 +88,7 @@
 
 A `return` statement without arguments returns the current values of the results. This is known as a "naked" return.
 
-Naked return statements should be used only in short function, as with the example shown here. They can harm readability in longer functions.
+Naked return statements should be used only in short functions, as with the example shown here. They can harm readability in longer functions.
 
 .play basics/named-results.go