Normalize Cached Xcode to lowercase string

[jerrymarino]

Currently, Apple yields a file of the name Xcode_VERSION.xip. When
loading this file from a cache, xcversion should be able to pick that
up.

It simply picks up the cached file by using a lowercase version of the
string.

[supermarin]

@joshdholtz @KrauseFx whoever owns this, FASTLANE_PASSWORD needs to be updated:

Please provide your Apple Developer Program account credentials
The login information you enter will be stored in your macOS Keychain
You can also pass the password using the `FASTLANE_PASSWORD` environment variable
See more information about it on GitHub: https://github.com/fastlane/fastlane/tree/master/credentials_manager

[joshdholtz]

@supermarin Thanks for noticing that! Hope all is well 😊

@milch Looks like you set that account up for the CI 🙃 Would you mind updating that whenever you are back at your computer working?

[milch]

The ENV vars are set up correctly, it looks like it's just what @Kesin11 mentioned in #383

We should probably just merge that PR so the E2E tests are disabled, as nice as having them would be