build: stop support building addons with VS 2013

PR-URL: https://github.com/nodejs/node/pull/14764
Refs: https://github.com/nodejs/node/pull/14730#issuecomment-321609328
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

BUILDING.md

@@ -70,9 +70,7 @@ Depending on host platform, the selection of toolchains may vary.
 
 #### Windows
 
-* Building Node: Visual Studio 2015 or Visual C++ Build Tools 2015 or newer
-* Building native add-ons: Visual Studio 2013 or Visual C++ Build Tools 2015
-  or newer
+* Visual Studio 2015 or Visual C++ Build Tools 2015 or newer
 
 ## Building Node.js on supported platforms