cmd/gobind: fix a typo that is missing quote at end

Change-Id: I91ffbda9c8f562bc66b75ca8a6360196d41c1b28
Reviewed-on: https://go-review.googlesource.com/74610
Reviewed-by: Elias Naur <elias.naur@gmail.com>
diff --git a/cmd/gobind/doc.go b/cmd/gobind/doc.go
index 32965b5..92f64ac 100644
--- a/cmd/gobind/doc.go
+++ b/cmd/gobind/doc.go
@@ -204,7 +204,7 @@
 
 Similarly, to import NSDate and call the static method [NSDate date]:
 
-	import "ObjC/Foundation/NSDate
+	import "ObjC/Foundation/NSDate"
 
 	d := NSDate.Date()