design/16339-alias-decls.md: fix minor typo

Change-Id: I865aa0622fc503653e1c84e6db8c1ed19c23005f
Reviewed-on: https://go-review.googlesource.com/26970
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/design/16339-alias-decls.md b/design/16339-alias-decls.md
index 7e1a19e..83800f3 100644
--- a/design/16339-alias-decls.md
+++ b/design/16339-alias-decls.md
@@ -371,7 +371,7 @@
 many tools. For instance, type switches assuming only the kinds of objects now
 in existence in go/types would need to be extended to handle aliases, should
 they show up in the public API. The go/types’ Info.Uses map, which currently
-mapes identifiers to objects, will require especial attention: Should it record
+maps identifiers to objects, will require especial attention: Should it record
 the alias to object references, or only the original names?
 
 At first glance, since an alias is simply another name for an object, it would