Release v2.5.1

#187 Don't parse 204 No Content responses because of a change in PHP 7's json_decode()

This will be the final version that supports PHP 5.3, 5.4 and 5.5.

Although this version should work with PHP 7 you may have issues with incompatible dependencies such as phpunit which require a lower PHP version. The next version will be v3 and will have complete support for PHP 7.