Core - Cef.ChromiumVersion change to using System.Version

- After upgrading to VS `17.12.1` the String::Format code wouldn't compile
 in .Net Core 3.1

Author: amaitland

CefSharp.Core.Runtime/Cef.h

@@ -131,10 +131,9 @@ namespace CefSharp
             {
                 String^ get()
                 {
-                    // Need explicit cast here to avoid C4965 warning when the minor version is zero.
-                    return String::Format("{0}.{1}.{2}.{3}",
-                        CHROME_VERSION_MAJOR, (Object^)CHROME_VERSION_MINOR,
-                        CHROME_VERSION_BUILD, CHROME_VERSION_PATCH);
+                    auto version = gcnew Version(CHROME_VERSION_MAJOR, CHROME_VERSION_MINOR, CHROME_VERSION_BUILD, CHROME_VERSION_PATCH);
+
+                    return version->ToString();
                 }
             }