Add composer 1.7.3, remove composer 1.7.2
Add composer 1.7.3, remove composer 1.7.2

for stack(s) cflinuxfs2, cflinuxfs3 [#161644852]

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