add php7 to travis build matrix
add php7 to travis build matrix

sphereio/sphere-php-sdk,sphereio/sphere-php-sdk,sphereio/commercetools-php-sdk,sphereio/sphere-php-sdk,sphereio/commercetools-php-sdk,sphereio/sphere-php-sdk,sphereio/commercetools-php-sdk,sphereio/commercetools-php-sdk