message: Fix markdown in docs
diff: @@ -196,7 +196,7 @@ build setting for novice users.
  shared `libmongoc` and static `mongocxx` is not supported, nor is
  linking against both static `libmongoc` and shared `mongocxx`.
  -For building with Visual Studio 2017 (without a C++17 polyfill), it is necessary to configure with an additional option, "/Zc:__cplusplus" to opt into the correct definition of `__cplusplus` ([problem described here](https://blogs.msdn.microsoft.com/vcblog/2018/04/09/msvc-now-correctly-reports-__cplusplus/)):
  +For building with Visual Studio 2017 (without a C++17 polyfill), it is necessary to configure with an additional option, `/Zc:__cplusplus` to opt into the correct definition of `__cplusplus` ([problem described here](https://blogs.msdn.microsoft.com/vcblog/2018/04/09/msvc-now-correctly-reports-__cplusplus/)):
  ```sh
  'C:\Program Files (x86)\CMake\bin\cmake.exe' -G "Visual Studio 15 2017 Win64"
  