Add 8.3.x branch, and use PHP 7.1 for the new branch.

[skyred]

The first release of Drupal 8.3.x arrives: https://www.drupal.org/project/drupal/releases/8.3.0-alpha1

For the new branch, we'd like to use PHP 7.1, for all the remaining/open PHP 7.1 compatibility issues (including all contributed modules), please see this tag on Drupal.org https://www.drupal.org/project/issues/search?projects=&project_issue_followers=&status%5B%5D=Open&issue_tags_op=%3D&issue_tags=PHP+7.1

As right now, there is only one unconfirmed bug report against Drupal Core on PHP 7.1, also since 8.3.x is still in alpha, it's perfectly safe to use PHP 7.1. In the near future, PHP 7.1 will be backport to 8.2.x image, once it's officially documented.

[yosifkit]

$ git --no-pager diff --no-index 8.2/ 8.3/
diff --git a/8.2/apache/Dockerfile b/8.3/apache/Dockerfile
index ab3efb8..aa13122 100644
--- a/8.2/apache/Dockerfile
+++ b/8.3/apache/Dockerfile
@@ -1,5 +1,5 @@
 # from https://www.drupal.org/requirements/php#drupalversions
-FROM php:7.0-apache
+FROM php:7.1-apache
 
 RUN a2enmod rewrite
 
@@ -23,8 +23,8 @@ RUN { \
 WORKDIR /var/www/html
 
 # https://www.drupal.org/node/3060/release
-ENV DRUPAL_VERSION 8.2.6
-ENV DRUPAL_MD5 57526a827771ea8a06db1792f1602a85
+ENV DRUPAL_VERSION 8.3.0-alpha1
+ENV DRUPAL_MD5 601f931d5a3281214917e3eabfd86408
 
 RUN curl -fSL "https://ftp.drupal.org/files/projects/drupal-${DRUPAL_VERSION}.tar.gz" -o drupal.tar.gz \
 	&& echo "${DRUPAL_MD5} *drupal.tar.gz" | md5sum -c - \
diff --git a/8.2/fpm/Dockerfile b/8.3/fpm/Dockerfile
index b366eda..3e1d501 100644
--- a/8.2/fpm/Dockerfile
+++ b/8.3/fpm/Dockerfile
@@ -1,5 +1,5 @@
 # from https://www.drupal.org/requirements/php#drupalversions
-FROM php:7.0-fpm
+FROM php:7.1-fpm
 
 # install the PHP extensions we need
 RUN apt-get update && apt-get install -y libpng12-dev libjpeg-dev libpq-dev \
@@ -21,8 +21,8 @@ RUN { \
 WORKDIR /var/www/html
 
 # https://www.drupal.org/node/3060/release
-ENV DRUPAL_VERSION 8.2.6
-ENV DRUPAL_MD5 57526a827771ea8a06db1792f1602a85
+ENV DRUPAL_VERSION 8.3.0-alpha1
+ENV DRUPAL_MD5 601f931d5a3281214917e3eabfd86408
 
 RUN curl -fSL "https://ftp.drupal.org/files/projects/drupal-${DRUPAL_VERSION}.tar.gz" -o drupal.tar.gz \
 	&& echo "${DRUPAL_MD5} *drupal.tar.gz" | md5sum -c - \