Install Latest Composer

Check the latest version apt have,

apt-cache policy composer

If it's not the version you want,

 First,

php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
HASH=`curl -sS https://composer.github.io/installer.sig`
php -r "if (hash_file('SHA384', 'composer-setup.php') === '$HASH') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"

Then,

sudo mv composer.phar /usr/local/bin/
alias composer='/usr/local/bin/composer.phar'