Downgrade composer to 1.5.0 for PHP 7.0

php-7.0/Dockerfile

@@ -91,7 +91,7 @@ RUN mkdir -p /root/.ssh && \
     \
     wget -q https://getcomposer.org/composer.phar -O /usr/local/bin/composer && \
     chmod +x /usr/local/bin/composer && \
-    composer selfupdate && \
+    composer selfupdate 1.5.0 && \
     \
     git clone https://github.com/tj/git-extras.git && \
     cd git-extras && \