Updated filepicker deps and update picker call

[garlicPasta]

Connection with issue(s)

FilePicker.platform.pickFiles changed to FilePicker.pickFiles in most recent filepicker version.

Solution description

updated dependency and correct picker call

[deandreamatias]

Had one error when compile on Android. Maybe for old version of Android setup
If you can solve, I will really appreciate.

/Users/runner/work/form_builder_file_picker/form_builder_file_picker/example/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java:19: error: cannot find symbol
      flutterEngine.getPlugins().add(new com.mr.flutter.plugin.filepicker.FilePickerPlugin());
                                                                         ^
  symbol:   class FilePickerPlugin
  location: package com.mr.flutter.plugin.filepicker
1 error

[garlicPasta]

Seems like that the maintainer of file picker undone this breaking change anyway. So i will close this. Thanks for the fast response!