pin docker images to PHP 7.2

contrib/docker/Dockerfile.apache

@@ -1,4 +1,4 @@
-FROM php:7-apache
+FROM php:7.2-apache
 
 ARG COMPOSER_VERSION="1.6.5"
 ARG COMPOSER_CHECKSUM="67bebe9df9866a795078bb2cf21798d8b0214f2e0b2fd81f2e907a8ef0be3434"

contrib/docker/Dockerfile.fpm

@@ -1,4 +1,4 @@
-FROM php:7-fpm
+FROM php:7.2-fpm
 
 ARG COMPOSER_VERSION="1.6.5"
 ARG COMPOSER_CHECKSUM="67bebe9df9866a795078bb2cf21798d8b0214f2e0b2fd81f2e907a8ef0be3434"