manually updates default php version
manually updates default php version

Co-authored-by: An Yu <446e9838deaeb979640d56c46523b7c882d598cd@pivotal.io>

cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cf-identity/php-buildpack,cloudfoundry/php-buildpack,cf-identity/php-buildpack,cf-identity/php-buildpack,cloudfoundry/php-buildpack,cf-identity/php-buildpack,cloudfoundry/php-buildpack,cloudfoundry/php-buildpack,cf-identity/php-buildpack,cf-identity/php-buildpack,cf-identity/php-buildpack