Confusing printing of types

```
julia> using Unitful: FreeUnits, s, 𝐓

julia> typeof(s)
FreeUnits{(s,), 𝐓, nothing}

julia> s isa FreeUnits{(s,), 𝐓, nothing}
false
```

I guess there's a distinction between `FreeUnits` and `Unit`, but they both print the same way.