message: Fix VS mention in README to 2017 after
diff: @@ -70,7 +70,7 @@ They can be installed with Homebrew and macos/Brewfile:
  brew bundle --file=macos/Brewfile
  - Windows using Visual Studio 2015
  + Windows using Visual Studio 2017
  ----------------------------------
  You need a full git checkout to build on Windows; see below for details.
  