Script cache creating is broken after bumping v8 version to 6.6.313

[pinepain]

It was known to be working in 6.6.275, however in 6.6.313 we have caching broken (https://travis-ci.org/pinepain/php-v8/jobs/345791065#L3109) - all tests return NULL for generated cache. I guess we need to make minimal example to reproduce and validate whether it's not a some obvious integration issue and then ask v8-users for help.

[pinepain]

Here's a deal breaker - v8/v8@5a68df2