Remove specific version importers and use the default one

importer18.go

@@ -1,16 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build !go1.9
-
-package main
-
-import (
-	"go/importer"
-	"go/types"
-)
-
-func defaultImporter() types.Importer {
-	return importer.Default()
-}

importer19.go

@@ -1,16 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build go1.9
-
-package main
-
-import (
-	"go/importer"
-	"go/types"
-)
-
-func defaultImporter() types.Importer {
-	return importer.For("source", nil)
-}

stringer.go

@@ -18,6 +18,7 @@ import (
 	"go/build"
 	exact "go/constant"
 	"go/format"
+	"go/importer"
 	"go/parser"
 	"go/token"
 	"go/types"
@@ -262,7 +263,7 @@ func (g *Generator) parsePackage(directory string, names []string, text interfac
 // check type-checks the package. The package must be OK to proceed.
 func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) {
 	pkg.defs = make(map[*ast.Ident]types.Object)
-	config := types.Config{Importer: defaultImporter(), FakeImportC: true}
+	config := types.Config{Importer: importer.Default(), FakeImportC: true}
 	info := &types.Info{
 		Defs: pkg.defs,
 	}