Dub now supports a `minDubVersion` field.

This field will abort the build if the user doesn't have a recent enough version of dub
and miss needed feature to perform the build.

`minDubVersion` can be added to project's `dub.json`:
-------
{
    ...
    "minDubVersion": "1.10"
    ...
}
------
or `dub.sdl`:
------
minDubVersion "1.10"
------