fixed importer

stringer.go

@@ -64,7 +64,9 @@ import (
 	"fmt"
 	"go/ast"
 	"go/build"
+	exact "go/constant"
 	"go/format"
+	"go/importer"
 	"go/parser"
 	"go/token"
 	"go/types"
@@ -74,10 +76,6 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
-
-	exact "go/constant"
-
-	_ "go/importer"
 )
 
 var (
@@ -270,7 +268,7 @@ 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{FakeImportC: true}
+	config := types.Config{Importer: importer.Default(), FakeImportC: true}
 	info := &types.Info{
 		Defs: pkg.defs,
 	}