file上传文件类型

application：zip、pdf、doc
image：jpg、png，bmp
audio：mp3、wav、ogg
video：mp4
text：txt、csv、css、html

accept={'image/png,image/jpeg,image/gif,image/jpg,video/mp4,
video/m3u8,video/flv,video/f4v,video/webm,video/mov,
video/m4v,video/3gp,video/avi,video/wmv'}