update example

example/example.js

 var am_xlsx2json = require('../')
 
 am_xlsx2json({
-  input: __dirname + '/testExcel.xlsx',
-  output: __dirname + '/testExcel.json'
+  input: __dirname + '/place-sample.xls',
+  output: __dirname + '/output.json'
 }, function(err, result) {
   if(err) {
     console.error(err);