Check only part of the error message as it's different in hhvm

tests/Composer/Test/Util/ErrorHandlerTest.php

@@ -38,7 +38,7 @@ class ErrorHandlerTest extends TestCase
      */
     public function testErrorHandlerCaptureWarning()
     {
-        $this->setExpectedException('\ErrorException', 'array_merge(): Argument #2 is not an array');
+        $this->setExpectedException('\ErrorException', 'array_merge');
 
         ErrorHandler::register();