fix autoload by removing static entry for Yii.php;

added include to new tests/_bootstrap.php instead

see https://github.com/yiisoft/yii2/issues/12885#issuecomment-257523695

composer.json

@@ -18,9 +18,6 @@
     "autoload": {
         "psr-4": {
             "fphammerle\\yii2\\auth\\clientcert\\": ""
-        },
-        "files": [
-            "vendor/yiisoft/yii2/Yii.php"
-        ]
+        }
     }
 }

phpunit.xml

@@ -1,4 +1,4 @@
-<phpunit bootstrap="vendor/autoload.php">
+<phpunit bootstrap="tests/_bootstrap.php">
   <testsuites>
     <testsuite name="helpers">
       <directory>tests</directory>

tests/_bootstrap.php

@@ -0,0 +1,4 @@
+<?php
+
+require_once __DIR__ . '/../vendor/autoload.php';
+require_once __DIR__ . '/../vendor/yiisoft/yii2/Yii.php';