Countries v1.8.0

Additions

add Slovak translations
add Chinese translations
add Dutch translation for Kosovo
add German translations for Kosovo and Curaçao

Build

add composer.lock file to prevent dependencies issues
allow setting a custom command name

Fixes

fix native name for Nepal (from apilayer/restcountries#23)
change demonym for Argentina to Argentine
fix demonym for Christmas Island
fix subregion in Slovak Republic
replace all "cmn" with "zho"
replaced Kosovo's International Olympic Committee code by ISO 3166-1 alpha-3 code in land borders array