doc: fix typo in types tutorial (closed -> close)

Fixes github.com/cuelang/cuelang.org/issues/118

Change-Id: Ib0391938f5182775704b90b4a02393d5f28bd0f8
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/8066
Reviewed-by: Paul Jolly <paul@myitcv.org.uk>
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
diff --git a/doc/tutorial/basics/2_types/50_closed.txt b/doc/tutorial/basics/2_types/50_closed.txt
index 50b3ade..a79edac 100644
--- a/doc/tutorial/basics/2_types/50_closed.txt
+++ b/doc/tutorial/basics/2_types/50_closed.txt
@@ -14,7 +14,7 @@
 In other words, closing a struct is equivalent to requiring that all
 other values be undefined.
 
-A closed struct can be created using the `closed` builtin,
+A closed struct can be created using the `close` builtin,
 but are more commonly defined using a _definition_, defined next.
 
 -- structs.cue --