Add missing (*Entry) Warning() function

entry.go

@@ -126,6 +126,10 @@ func (entry *Entry) Warn(args ...interface{}) {
 	}
 }
 
+func (entry *Entry) Warning(args ...interface{}) {
+	entry.Warn(args...)
+}
+
 func (entry *Entry) Error(args ...interface{}) {
 	if entry.Logger.Level >= ErrorLevel {
 		entry.log(ErrorLevel, fmt.Sprint(args...))