15292/2013-12-type-params.md: fix quoting in example

Change-Id: Ie14866e03b569cfdb9c417b06fa593b0509d0092
Reviewed-on: https://go-review.googlesource.com/22280
Reviewed-by: Minux Ma <minux@golang.org>
diff --git a/design/15292/2013-12-type-params.md b/design/15292/2013-12-type-params.md
index 832060f..1a58320 100644
--- a/design/15292/2013-12-type-params.md
+++ b/design/15292/2013-12-type-params.md
@@ -480,7 +480,7 @@
 import (
 	"fmt"
 	"hashmap"
-	"os'
+	"os"
 )
 
 func hashint(i int) uint {