Bump php from 5.6-fpm-alpine to 8.2-fpm-alpine in /docker

Bumps php from 5.6-fpm-alpine to 8.2-fpm-alpine.

---
updated-dependencies:
- dependency-name: php
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

docker/Dockerfile

@@ -20,7 +20,7 @@ RUN set -eux \
     && bower install --production --allow-root --silent
 
 
-FROM php:5.6-fpm-alpine as php
+FROM php:8.2-fpm-alpine as php
 
 ENV TERM="xterm-256color" \
 LANGUAGE="en_US.UTF-8" \