Switch Composer Hash to file_get_contents()

Author: michaelw90

Dockerfile

@@ -3,7 +3,7 @@ FROM php:7.3-cli
 RUN apt-get update && apt-get -y install zip unzip
 
 RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
-RUN php -r "if (hash_file('sha384', 'composer-setup.php') === 'e5325b19b381bfd88ce90a5ddb7823406b2a38cff6bb704b0acc289a09c8128d4a8ce2bbafcd1fcbdc38666422fe2806') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
+RUN php -r "if (hash_file('sha384', 'composer-setup.php') === file_get_contents('https://composer.github.io/installer.sig')) { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
 RUN php composer-setup.php
 RUN php -r "unlink('composer-setup.php');"