In your composer file you are using ~5.4, which causes composer to fail when using PHP7. I assume there is not reason that the package should not be used on PHP7? If not I suggest to change to >=5.4
Error when running composer:
umpirsky/country-list dev-master requires php ~5.4 -> your PHP version (7.0.2) does not satisfy that requirement
In your composer file you are using ~5.4, which causes composer to fail when using PHP7. I assume there is not reason that the package should not be used on PHP7? If not I suggest to change to >=5.4
Error when running composer:
umpirsky/country-list dev-master requires php ~5.4 -> your PHP version (7.0.2) does not satisfy that requirement