Ninja Forms - File Uploads Addon 3.3.20

*Bugs:*

* Fatal error: Cannot redeclare pcntl_signal() on some install

*Bugs:*

* Select File button not working on Internet Explorer 11 still

*New:*

* You can now use mergetags in the 'Rename Uploaded File' field setting
* Different mergetags for File Upload fields can now be selected, eg. {field:my_field_key:link}
* New mergetag for the filename of the file, eg. {field:my_field_key:filename}
* New mergetags for when the file has been added to the media library, eg. {field:my_field_key:attachment_url}, {field:my_field_key:attachment_embed}

*Changes:*

* Ability to set Amazon key and secret and other settings as constants: 'NF_FU_AMAZON_S3_ACCESS_KEY' and 'NF_FU_AMAZON_S3_SECRET_KEY'

*Bugs:*

* Nonce error when submitting a form on a page that has been cached
* Fatal error caused when running UpdraftPlus or BackupBuddy plugin