CopyToOutputDirectory does not propagate to package

### Steps to reproduce
- Create ClassLibrary1
- Add a folder called "Files"
- Add a file to the folder
- Include the following in the `.csproj`:
```


Always


```
- Run `dotnet pack ClassLibrary1.csproj`
- Add this package to a local NuGet source

- Create ClassLibrary2
- Include ClassLibrary1 package
- Build
- "Files" will not be in output

### Expected behavior
"Files" should be in output directory of ClassLibrary2

### Actual behavior
It is not

### Environment data
`msbuild /version` output:

Microsoft (R) Build Engine version 15.6.85.37198 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

15.6.85.37198

OS info:
Windows 10 Enterprise
Visual Studio 2017