use jet v5.0.2 (no breaking changes)

relative to: https://github.com/kataras/iris/pull/1616

i18n/loader.go

@@ -7,7 +7,6 @@ import (
 	"io/ioutil"
 	"path/filepath"
 	"strings"
-	"sync"
 	"text/template"
 
 	"github.com/kataras/iris/v12/context"
@@ -266,11 +265,6 @@ type defaultLocale struct {
 	defaultMessageFunc MessageFunc
 }
 
-type templateKey struct {
-	Template *template.Template
-	once     *sync.Once
-}
-
 func (l *defaultLocale) Index() int {
 	return l.index
 }