use legacy phpunit test classes for php 5.5.9

Author: Sam Stevens

Tests/Callbacks/UserSettingCallbackTest.php

@@ -4,7 +4,7 @@
 
 use Bugsnag\BugsnagBundle\Callbacks\UserSettingCallback;
 use Bugsnag\Report;
-use PHPUnit\Framework\TestCase;
+use PHPUnit_Framework_TestCase as TestCase;
 use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorageInterface;
 use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
 use Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface;

Tests/DependencyInjection/Compiler/CallbackRegisteringPassTest.php

@@ -4,7 +4,7 @@
 
 use Bugsnag\BugsnagBundle\DependencyInjection\Compiler\CallbackRegisteringPass;
 use Bugsnag\Client;
-use PHPUnit\Framework\TestCase;
+use PHPUnit_Framework_TestCase as TestCase;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Reference;