Update zh-tw.js

most taiwanese prefer numerical month date format instead chinese characters, same as zh-cn.
current zh-tw only display month in chinese character 
http://cdn.knightlab.com/libs/timeline/latest/embed/index.html?source=0AlHbrYHut1HUdGNNamt6QzdDeFFyMXVFRmtsUmp4TFE&font=Bevan-PotanoSans&maptype=toner&lang=zh-tw&height=650