Update README.md for 51.0.0 release

Author: amaitland

README.md

@@ -59,8 +59,8 @@ Every commit on `master` produces a `Nuget` package. Use at your own risk! [CefS
 | Branch | CEF Version | VC++ Version | .Net Version | Status |
 |--------|-------------|--------------|--------------|--------|
 | [master](https://github.com/cefsharp/CefSharp/) | 2704 | 2013 | 4.5.2 | Development |
-| [cefsharp/51](https://github.com/cefsharp/CefSharp/tree/cefsharp/51) | 2704 | 2013 | 4.5.2 | Pre-Release |
-| [cefsharp/49](https://github.com/cefsharp/CefSharp/tree/cefsharp/49) | 2623 | 2013 | 4.0   | **Release** |
+| [cefsharp/51](https://github.com/cefsharp/CefSharp/tree/cefsharp/51) | 2704 | 2013 | 4.5.2 | **Release** |
+| [cefsharp/49](https://github.com/cefsharp/CefSharp/tree/cefsharp/49) | 2623 | 2013 | 4.0   | Unsupported |
 | [cefsharp/47](https://github.com/cefsharp/CefSharp/tree/cefsharp/47) | 2526 | 2013 | 4.0   | Unsupported |
 | [cefsharp/45](https://github.com/cefsharp/CefSharp/tree/cefsharp/45) | 2454 | 2013 | 4.0   | Unsupported |
 | [cefsharp/43](https://github.com/cefsharp/CefSharp/tree/cefsharp/43) | 2357 | 2012 | 4.0   | Unsupported |