Drop PHP 5.6 support

Since the code already uses the return types there is no way of running this in PHP 5.6

Author: Nico Stapelbroek

.travis.yml

@@ -1,13 +1,10 @@
 language: php
+sudo: false
 
 jobs:
   include:
   - stage: Unit tests
-  - env:
-    php: 5.6
-  - env: COMPOSER_FLAGS="--prefer-lowest"
-    php: 5.6
-  - env:
+    env:
     php: 7.0
   - env: COMPOSER_FLAGS="--prefer-lowest"
     php: 7.0

composer.json

@@ -13,7 +13,7 @@
         }
     ],
     "require": {
-        "php": "^5.6 || ^7.0",
+        "php": ">=7.0",
         "sentry/sentry": "^1.9.2",
         "zendframework/zend-eventmanager": "^2.5|| ^3.0",
         "zendframework/zend-mvc": "^2.5 || ^3.0",