Case sensitivity bug on linux

[Klaus Frank]

Currently this module fails because of a very small bug.
Linux systems are case sensitive, where windows is not.
Currently this module throws an error on linux:

Add-Type : Cannot bind parameter 'Path' to the target. Exception setting "Path": "Cannot find path '/usr/local/share/powershell/Modules/PSExcel/1.0.2/lib/epplus.dll' because it does not ex
ist."
At /usr/local/share/powershell/Modules/PSExcel/1.0.2/PSExcel.psm1:9 char:41
+     if( -not ($Library = Add-Type -path $BinaryPath -PassThru -ErrorA ...
+                                         ~~~~~~~~~~~
+ CategoryInfo          : WriteError: (:) [Add-Type], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : ParameterBindingFailed,Microsoft.PowerShell.Commands.AddTypeCommand

The fix is to replace the lowercase filename inside of PSExcel.psm1