Update install instructions for VS 2019 (#736)

Author: steveklabnik

templates/tools/install.hbs

@@ -87,12 +87,12 @@
         On Windows, Rust additionally requires the C++ build tools
         for Visual Studio 2013 or later. The easiest way to acquire the build
         tools is by installing
-        <a href="https://www.visualstudio.com/downloads/#build-tools-for-visual-studio-2017">
-          Microsoft Visual C++ Build Tools 2017
+        <a href="https://www.visualstudio.com/downloads/#build-tools-for-visual-studio-2019">
+          Microsoft Visual C++ Build Tools 2019
         </a>
         which provides just the Visual C++ build tools. Alternately, you
         can <a href="https://www.visualstudio.com/downloads/">install</a>
-        Visual Studio 2017, Visual Studio 2015, or Visual Studio 2013 and during install select
+        Visual Studio 2019, Visual Studio 2017, Visual Studio 2015, or Visual Studio 2013 and during install select
         the “C++ tools.”
       </p>
       <p>