Fails to compile on Windows

On Windows, `npm install` fails with the following error:

```
c:\work\ad-block\protocol.cc(57): error C2429: attribute 'fallthrough' requires compiler flag '/std:c++17' [C:\work\ad-block\build\ad-block.vcxproj]
c:\work\ad-block\protocol.cc(115): error C2429: attribute 'fallthrough' requires compiler flag '/std:c++17' [C:\work\ad-block\build\ad-block.vcxproj]
```
