Fixed the spec checking for private method on HHVM
Fixed the spec checking for private method on HHVM

HHVM does not yet define the private __clone method on ReflectionClass, so
the spec was failing. The HHVM incompatibility has been reported as
https://github.com/facebook/hhvm/issues/1572

jakari/prophecy,kamioftea/prophecy,ftrrtf/prophecy,dantleech/prophecy,jakzal/prophecy,Taluu/prophecy,phpspec/prophecy