fix issue 351

[Misiu]

Lower Microsoft.CodeAnalysis.CSharp version to 4.5.0 to fix the update issue. Closes #351

I've run all the tests and all of them passed. I've created a local package and was able to update Carter in my project.

[CollinAlpert]

Please check if #355 fixes this issue first, that would be the preferred fix to lowering the M.CA.C version.

[JoeStead]

Closing this as a fix has been put in to address the underlying issue