(GH-232) Pack includes files from nuspec directory

Instead of starting at the current directory to use files for the nuspec, use
the nuspec directory as the starting path to look at files.

src/chocolatey/infrastructure.app/services/NugetService.cs

@@ -146,7 +146,7 @@ public void pack_run(ChocolateyConfiguration config)
             // Initialize the property provider based on what was passed in using the properties flag
             var propertyProvider = new DictionaryPropertyProvider(properties);
 
-            var basePath = _fileSystem.get_current_directory();
+            var basePath = nuspecDirectory;
             if (config.Information.PlatformType != PlatformType.Windows)
             {
                 //bug with nuspec and tools/** folder location on Windows.