Skip redis tests until PHP7.2 stabilizes

This will let us get passing builds out of PHP7.2 and hopefully make
changes in future beta's more visible.

.travis.yml

@@ -33,9 +33,6 @@ cache:
 matrix:
   fast_finish: true
 
-  allow_failures:
-    - php: 7.2
-
   include:
     - php: 7.0
       env: PHPCS=1 DEFAULT=0

tests/TestCase/Cache/Engine/RedisEngineTest.php

@@ -33,6 +33,7 @@ class RedisEngineTest extends TestCase
     {
         parent::setUp();
         $this->skipIf(!class_exists('Redis'), 'Redis extension is not installed or configured properly.');
+        $this->skipIf(version_compare(PHP_VERSION, '7.2.0beta', '>='), 'Redis is misbehaving in PHP7.2');
 
         // @codingStandardsIgnoreStart
         $socket = @fsockopen('127.0.0.1', 6379, $errno, $errstr, 1);