Update licenses.txt and notices

Author: Arin Ghazarian

.licenses/licenses.txt

@@ -212,7 +212,7 @@ Copyright © Microsoft Corporation.  All rights reserved.
 License available at https://github.com/dotnet/corefx/blob/master/LICENSE.TXT
 
 
-License notice for YamlDotNet (v13.7.1)
+License notice for YamlDotNet (v15.1.2)
 ------------------------------------
 
 https://github.com/aaubry/YamlDotNet.git

ThirdPartyNotices.txt

@@ -340,7 +340,7 @@ SOFTWARE.
 
 ---------------------------------------------------------
 
-YamlDotNet 13.7.1 - MIT
+YamlDotNet 15.1.2 - MIT
 https://github.com/aaubry/YamlDotNet.git
 
 Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Antoine Aubry and contributors