--- a/wp/Dockerfile	Tue Apr 23 20:28:37 2019 +0200
+++ b/wp/Dockerfile	Wed Apr 24 02:17:42 2019 +0200
@@ -55,6 +55,8 @@
     }" \
  && php /tmp/installer.php --no-ansi --install-dir=/usr/bin --filename=composer --version=${COMPOSER_VERSION} \
  && composer --ansi --version --no-interaction \
+# install prestissimo composer parallel install plugin.
+ && composer --no-interaction global require --no-progress hirak/prestissimo \
  && rm -f /tmp/installer.php