Update README.md

Author: andrey-helldar

README.md

@@ -3,7 +3,6 @@
 ![Luhn-algorithm card-number](https://preview.dragon-code.pro/Luhn's-algorithm/card-number.svg?brand=php&preposition=with)
 
 [![Stable Version][badge_stable]][link_packagist]
-[![Unstable Version][badge_unstable]][link_packagist]
 [![Total Downloads][badge_downloads]][link_packagist]
 [![License][badge_license]][link_license]
 
@@ -351,8 +350,6 @@ This package is licensed under the [MIT License](LICENSE).
 
 [badge_stable]:     https://img.shields.io/github/v/release/TheDragonCode/card-number?label=stable&style=flat-square
 
-[badge_unstable]:   https://img.shields.io/badge/unstable-dev--main-orange?style=flat-square
-
 [link_license]:     LICENSE
 
 [link_packagist]:   https://packagist.org/packages/dragon-code/card-number