message: Update appveyor to Rust 1.16
diff: environment:
  matrix:
  - - TARGET: 1.14.0-x86_64-pc-windows
  + - TARGET: 1.16.0-x86_64-pc-windows
  COMPILER: gnu
  - - TARGET: 1.14.0-x86_64-pc-windows
  + - TARGET: 1.16.0-x86_64-pc-windows
  COMPILER: msvc
  install:
  - if %COMPILER%==gnu choco install -y mingw
  