Drop PHP 5.6 + 7.0 (#257)

* Drop PHP 5.6 + 7.0

* Remove `syntaxCheck`

* Add void

Author: ruudk

composer.json

@@ -23,15 +23,15 @@
     ],
     "homepage": "http://www.php-cache.com/en/latest/",
     "require": {
-        "php": "^5.6 || ^7.0 || ^8.0",
+        "php": "^7.1 || ^8.0",
         "cache/adapter-common": "^1.0",
         "cache/hierarchical-cache": "^1.0",
         "psr/cache": "^1.0 || ^2.0",
         "psr/simple-cache": "^1.0"
     },
     "require-dev": {
-        "cache/integration-tests": "^0.16",
-        "phpunit/phpunit": "^5.7.21"
+        "cache/integration-tests": "^0.17",
+        "phpunit/phpunit": "^7.5.20 || ^9.5.10"
     },
     "provide": {
         "psr/cache-implementation": "^1.0",

phpunit.xml.dist

@@ -8,7 +8,6 @@
   convertWarningsToExceptions="true"
   processIsolation="false"
   stopOnFailure="false"
-  syntaxCheck="false"
   bootstrap="vendor/autoload.php"
   >
   <testsuites>