Download failed: file_get_contents(): SSL operation failed with code 1. OpenSSL Error messages:
error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
file_get_contents(): Failed to enable crypto
file_get_contents(https://getcomposer.org/composer.phar): failed to open stream: operation failed
Downloading…

Fix:

apt-get install curl
php -r "readfile('http://getcomposer.org/installer');" | php