Include dice in RollResult

[Ainias]

Its basically the same PR as #252 but I added a check inside the setter.

Note that I only check for typeof dice !== 'object'
at first I had something like

if (!(dice instanceof StandardDice)){
  ...
}

but then I got dependency cycle errors of eslint and I don't think we can solve them without some serious redesign or ugly hacks. So I only included the typeof check