add crop btn support

Author: JackPu

README.md

@@ -80,6 +80,7 @@ Use CDN Script(ES5)
 | extensions | String | 'png,jpg,gif' | limit the file type |
 | crop | Boolean | true | if need crop image |
 | cropRatio | String | '1:1' | limit the cropped image shape|
+| cropBtn | Object | {ok:'Save','cancel':'Give Up'} | the text of crop button|
 | maxFileSize | Number | 10485760(10M) | limit the file size|
 | maxWidth | Number | 150 | limit the width of your image you cropped|
 | maxheight | Number | 150 | limit the height of your image you cropped|