Update go version

vendor/golang.org/x/tools/go/ssa/util.go

@@ -181,19 +181,13 @@ func newVar(name string, typ types.Type) *types.Var {
 	return types.NewParam(token.NoPos, nil, name, typ)
 }
 
-// anonVar creates an anonymous 'var' for use in a types.Tuple.
-func anonVar(typ types.Type) *types.Var {
-	return newVar("", typ)
-}
-
-var lenResults = types.NewTuple(anonVar(tInt))
+var lenResults = typesinternal.TupleOf(tInt)
 
 // makeLen returns the len builtin specialized to type func(T)int.
 func makeLen(T types.Type) *Builtin {
-	lenParams := types.NewTuple(anonVar(T))
 	return &Builtin{
 		name: "len",
-		sig:  types.NewSignatureType(nil, nil, nil, lenParams, lenResults, false),
+		sig:  types.NewSignatureType(nil, nil, nil, typesinternal.TupleOf(T), lenResults, false),
 	}
 }