fix(Template): correct check error

fs.go

@@ -40,7 +40,7 @@ func walk(fs http.FileSystem, path string, info os.FileInfo, walkFn filepath.Wal
 
 	dir, err := fs.Open(path)
 	defer dir.Close()
-	if err == nil {
+	if err != nil {
 		err1 := walkFn(path, info, err)
 		if err1 != nil {
 			return err1

template.go

@@ -206,7 +206,7 @@ func BuildTemplate(dir string, files ...string) error {
 		return self.visit(path, f, err)
 	})
 	if err != nil {
-		fmt.Printf("filepath.Walk() returned %v\n", err)
+		fmt.Printf("Walk() returned %v\n", err)
 		return err
 	}
 	buildAllFiles := len(files) == 0