Intro
As a precaution, NuGet has started adding requireReinstallation="true" attribute anytime the solution you're working with has been upgraded (or downgraded) to a different framework version than when it was originally installed. For example, you installed a third-party package when your project was targetting .NET Framework 4.6.1. And shortly thereafter, you upgrade your project to target .NET Framework 4.6.2.
What this means is that you will have warnings indicating that you have to reinstall these packages every time you do a build. To resolve this, you simply have to reinstall the package and hope that the third-party package supports the framework you just told your project to target.
Here's the command and link to the official article from Microsoft with more details on the matter:
Update-Package –reinstall <package_name>