Build command

Please, replace build command in `F#.sublime-build`. It should be
```
{
  "cmd": ["fsharpi", "$file"],
  "windows": {
    "cmd": ["dotnet", "fsi", "$file"]
  },
  "file_regex": "^((?:.*)\\.(?:fs(?:i|x)?))\$([0-9]*),([0-9]*)\$: (.*)$",
  "selector": "source.fsharp"
}
```
`fsi.exe` is supplied with Visual Studio, but `dotnet fsi myscript.fsx` is more generic and works w/o VS.
