Allowed failures on PHP 7.1 environments

.travis.yml

@@ -23,3 +23,8 @@ after_script:
   - php ocular.phar code-coverage:upload --format=php-clover build/clover.xml
 
 sudo: false
+
+matrix:
+  fast_finish: true
+  allow_failures:
+    - php: 7.1

module/Common/src/Factory/CacheFactory.php

@@ -59,10 +59,6 @@ class CacheFactory implements FactoryInterface
             case Cache\PhpFileCache::class:
                 return new $cacheConfig['adapter']($cacheConfig['options']['dir']);
             case Cache\MemcachedCache::class:
-                if (! class_exists(\Memcached::class)) {
-                    return new Cache\ArrayCache();
-                }
-
                 $memcached = new \Memcached();
                 $servers = isset($cacheConfig['options']['servers']) ? $cacheConfig['options']['servers'] : [];