correct method not called when adding one involving Type of Union

[rfourquet]

Sorry for the bad title (I lack vocabulary on that topic, please edit it). It looks like a #265 problem:

julia> foo(::Type{<:Union{Int8,Int,UInt}}) = 1;

julia> foo(Union{Int,UInt})
1

julia> foo(::Union) = 2; 

julia> foo(Union{Int,UInt})
1

julia> foo(Union{Int8,UInt})
2

julia> foo(Union{Int,UInt}) # now works correctly
2

[vtjnash]

Likely the same as #11840

[JeffBezanson]

Seems to work now. The first method is always more specific, and 1 is always returned.