go/types: fix typo

Fixes #18562

Change-Id: Ic195a8606f09876e2667e4ef720b84a07d316f4a
Reviewed-on: https://go-review.googlesource.com/34939Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/types/api.go

@@ -5,7 +5,7 @@
 // Package types declares the data types and implements
 // the algorithms for type-checking of Go packages. Use
 // Config.Check to invoke the type checker for a package.
-// Alternatively, create a new type checked with NewChecker
+// Alternatively, create a new type checker with NewChecker
 // and invoke it incrementally by calling Checker.Files.
 //
 // Type-checking consists of several interdependent phases: