updated to use cache with lucene.net 4.8 beta on .net standard 2.0 an…

[yohsii]

…d with latest azure blob library.

please try these changes, the cache is back.

[richorama]

Thank you.

I have merged your work into a branch on this repo. I'm trying to get the tests to work, then I'll hope to publish shortly after.

It'll probably take a few days, as I'm maxed out on other stuff.

[yohsii]

thanks @richorama you will need to pass in a valid cache directory path to the AzureDirectory constructor to get tests passing

[richorama]

see #34