encoding/openapi: correct typo

Change-Id: I864b86c333069e7e1cacf02ed9d140e13c29ad2a
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2461
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/encoding/openapi/build.go b/encoding/openapi/build.go
index 9b49b1f..eaa0df4 100644
--- a/encoding/openapi/build.go
+++ b/encoding/openapi/build.go
@@ -76,7 +76,7 @@
 
 	c := buildContext{
 		inst:         inst,
-		refPrefix:    "components/schema",
+		refPrefix:    "components/schemas",
 		expandRefs:   g.ExpandReferences,
 		nameFunc:     g.ReferenceFunc,
 		descFunc:     g.DescriptionFunc,