adding content in for package.config nuget

[PureWeen]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Added the content file back in for SQLitePersistentBlobCache linker preservation

What is the current behavior? (You can also link to an open issue here)
File wasn't included as content anaymore

What is the new behavior (if this is a feature change)?
The pp file is not included and gets added correctly into projects using older package.config structure

Does this PR introduce a breaking change?
it shouldn't

Please check if the PR fulfills these requirements

• The commit follows our guidelines: https://github.com/Akavache/Akavache/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

[PureWeen]

hunh this seems like a bug in the upstream tools

Error: The assembly 'Cake.PinNuGetDependency, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null' 
is referencing an older version of Cake.Core (0.17.0). 
This assembly need to reference at least Cake.Core version 0.22.0.

something with