Upgrade PHPUnit to version 5

- Fix deprecated getMock
- Use PHPUnit 4 for PHP 5.5 build

Manually cherry-picked from PR
https://github.com/wallabag/wallabag/pull/2201

tests/Wallabag/CoreBundle/EventListener/LocaleListenerTest.php

@@ -15,7 +15,11 @@ class LocaleListenerTest extends \PHPUnit_Framework_TestCase
 {
     private function getEvent(Request $request)
     {
-        return new GetResponseEvent($this->getMock('Symfony\Component\HttpKernel\HttpKernelInterface'), $request, HttpKernelInterface::MASTER_REQUEST);
+        $kernel = $this->getMockBuilder('Symfony\Component\HttpKernel\HttpKernelInterface')
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        return new GetResponseEvent($kernel, $request, HttpKernelInterface::MASTER_REQUEST);
     }
 
     public function testWithoutSession()