Fix case sensitivity bug on linux

[agowa]

Fixes #71

[RamblingCookieMonster]

Hiyo! Have you tried this? Does it actually work? I had thought EPPlus didn't support other platforms or .NET Core?

Happy to merge in a tiny change like this if so, but other than that, this is pretty much a dead project, ImportExcel is the way forward

Cheers!

[agowa]

I'm using this inside of a docker container (docker pull agowa338/vmware_deployment_runner) with the latest version of powershell core and it imported successfully. I've only tried it with only one document.

[agowa]

I'd a brief look at ImportExcel, it's not what I need. It does not work on PowerShell Core on Linux, it fails already at Import-Module, so I'll stay with your's until there's something working for PowerShell Core on Linux.