fix orientation option (#3405)

lib/timeline/Core.js

@@ -375,7 +375,9 @@ Core.prototype.setOptions = function (options) {
       }
     }
 
-    this.options.orientation = {item:undefined,axis:undefined};
+    if (typeof this.options.orientation !== 'object') {
+      this.options.orientation = {item:undefined,axis:undefined};
+    }
     if ('orientation' in options) {
       if (typeof options.orientation === 'string') {
         this.options.orientation = {