[finc] use latest php 7.2-fpm-alpine Docker

* avoid external validation problems with certificates using let's encrypt

devops/docker/php/Dockerfile

@@ -16,7 +16,7 @@
 # @author  Sebastian Kehr <kehr@ub.uni-leipzig.de>
 # @license https://opensource.org/licenses/GPL-3.0 GNU GPLv3
 
-FROM php:7.2.11-fpm-alpine3.8
+FROM php:7.2-fpm-alpine
 RUN apk add --no-cache $PHPIZE_DEPS freetype-dev libxml2-dev icu-dev libxslt-dev \
     && pecl install xdebug-2.9.6 \
     && docker-php-ext-enable xdebug \