Concurrent creation of a directory while unzipping leads to a missing libraries

Hi,
It looks like there we have to prepare `@config.generated_frameworks_dir` directory as well, otherwise it will be created by zip-tool concurrently and can lead to a missing library because of failed unzip.

https://github.com/grab/cocoapods-binary-cache/blob/b1896f30fe90c9660362d7a3361ed2cdbcc1d46b/lib/command/executor/fetcher.rb#L53