Update readme to reflect usage of VS2019 (#1469)

Author: WillEllis

README.md

@@ -39,7 +39,7 @@ Comprehensive and easy to use Material Design theme and control library for the
 * Checkout [Motion List](https://github.com/MaterialDesignInXAML/MotionList).
 
 # ![Alt text](web/images/MD4XAML28.png "How Can I Use The Themes?") Source Code
-To load the source project you will need Visual Studio 2017.  Don't worry if you have an earlier version, you can still use the compiled assemblies from NuGet (``` Install-Package MaterialDesignThemes ```). There are two demo projects in the solution, restore the necessary NuGet packages and correct the programming syntax that is not compatible with C# versions lower than C# 7.0 (```currently used in Visual Studio 2017```). Then, you should be able to fire both of these projects up.  One is a "pure" Material Design project, the other illustrates how to combine with Dragablz & MahApps.
+To load the source project you will need Visual Studio 2019.  Don't worry if you have an earlier version, you can still use the compiled assemblies from NuGet (``` Install-Package MaterialDesignThemes ```). There are two demo projects in the solution, restore the necessary NuGet packages and correct the programming syntax that is not compatible with C# versions lower than C# 8.0 (```currently used in Visual Studio 2019```). Then, you should be able to fire both of these projects up.  One is a "pure" Material Design project, the other illustrates how to combine with Dragablz & MahApps.
 
 # ![Alt text](web/images/MD4XAML28.png "Contributions") Contribution Guidelines