TASK: Adjust to PHP 7.1

* As PHP 7.1 is required, document and adjust tests in CI.

Relates: #71

.gitlab-ci.yml

@@ -27,7 +27,7 @@ sync:github:
     - git push --mirror ${MIRROR_GIT_URL}
 
 lint:coding-guideline: &PHP-LINTING
-  image: php:7.0-alpine
+  image: php:7.1-alpine
   stage: test
   script:
     - ./vendor/bin/phpcs -s -n --report-full=result/phpcs-full.txt --report-diff=result/phpcs-diff.txt --report-summary=result/phpcs-summary.txt
@@ -41,16 +41,12 @@ lint:php-mass-detection:
   script:
     - ./vendor/bin/phpmd src text phpmd.xml > result/phpmd.txt
 
-test:5.6: &PHP-UNITTESTING
-  image: php:5.6-alpine
+test:7.1: &PHP-UNITTESTING
+  image: php:7.1-alpine
   stage: test
   script:
     - ./vendor/bin/phpunit
 
-test:7.0:
-  <<: *PHP-UNITTESTING
-  image: php:7.0-alpine
-
 test:latest:
   <<: *PHP-UNITTESTING
   image: php:7-alpine

Documentation/source/index.rst

@@ -19,6 +19,8 @@ Requirements
 To install the project you need ``composer`` to be installed and inside your ``$PATH``.
 Otherwise run ``make install-composer`` to install composer.
 
+At least PHP 7.1 is required.
+
 Installation
 ============