use source for composer downloads and remove cached files/repos

Author: Jeremy Price

Dockerfile

@@ -110,7 +110,7 @@ COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
 
 # Get dependencies
 USER docker
-RUN composer install --no-dev --working-dir=/var/www/html
+RUN composer install --no-dev --working-dir=/var/www/html --prefer-source && rm -rf /var/www/html/vendor/*/.git && rm -rf /home/docker/.cache/composer
 USER root
 
 ############### APPLICATION INSTALL/INIT #################