(#502) Fix path separator in nuspec file element
(#502) Fix path separator in nuspec file element

Converts the path separator character in the nuspec file source to the
character that is correct for the OS that is running the packing
operation. Changes "\" to "/" on Linux and MacOS systems, and
changes "/" to "\" on Windows systems.

Fixes: https://github.com/chocolatey/choco/issues/502

chocolatey/nuget-chocolatey,chocolatey/nuget-chocolatey,chocolatey/nuget-chocolatey,chocolatey/nuget-chocolatey,chocolatey/nuget-chocolatey,chocolatey/nuget-chocolatey