`hls --version` does not work

[hasufell]

It starts building stuff instead of reporting the version and then exiting.

[fendor]

Indeed: https://github.com/haskell/haskell-language-server/blob/master/exe/Main.hs#L131
Looks like we are not terminating correctly

[hasufell]

In addition, there should be a --numeric-version opts that is machine-parsable and only prints the raw version.