WPForms Zapier Addon 1.6.0

### IMPORTANT
- Support for PHP 5.6 has been discontinued. If you are running PHP 5.6, you MUST upgrade PHP before installing WPForms Zapier 1.6.0. Failure to do that will disable WPForms Zapier functionality.
- Support for WordPress 5.4 and below has been discontinued. If you are running any of those outdated versions, you MUST upgrade WordPress before installing WPForms Zapier 1.6.0. Failure to do that will disable WPForms Zapier functionality.

### Added
- Compatibility with the upcoming WPForms 1.8.8.

### Changed
- Minimum WPForms version supported is 1.8.4.

### Changed
- Minimum WPForms version supported is 1.7.5.5.
- Updated Zapier logo.

### Fixed
- Incorrect URL to the documentation article was used on the Settings > Integrations page.
- Multi-select drowdown field options were not comma separated.
- '0' values were not processed correctly.
- Files were not properly uploaded to Zapier when more than 1 file was uploaded using a modern style file upload field.