The scitype of `[missing, missing]` should be Missing

[DilumAluthge]

Fixes #105

With this patch:

julia> import ScientificTypes

julia> import MLJScientificTypes

julia> ScientificTypes.set_convention(MLJScientificTypes.MLJ())

julia> ScientificTypes.scitype([1, 2])
AbstractVector{ScientificTypes.Count} = AbstractArray{ScientificTypes.Count,1}

julia> ScientificTypes.scitype([1.0, 2.0])
AbstractVector{ScientificTypes.Continuous} = AbstractArray{ScientificTypes.Continuous,1}

julia> ScientificTypes.scitype(["foo", "bar"])
AbstractVector{ScientificTypes.Textual} = AbstractArray{ScientificTypes.Textual,1}

julia> ScientificTypes.scitype([1, missing])
AbstractVector{Union{Missing, ScientificTypes.Count}} = AbstractArray{Union{Missing, ScientificTypes.Count},1}

julia> ScientificTypes.scitype([1.0, missing])
AbstractVector{Union{Missing, ScientificTypes.Continuous}} = AbstractArray{Union{Missing, ScientificTypes.Continuous},1}

julia> ScientificTypes.scitype(["foo", missing])
AbstractVector{Union{Missing, ScientificTypes.Textual}} = AbstractArray{Union{Missing, ScientificTypes.Textual},1}

julia> ScientificTypes.scitype([missing, missing])
AbstractVector{Missing} = AbstractArray{Missing,1}

julia> ScientificTypes.scitype(Missing[])
AbstractVector{Missing} = AbstractArray{Missing,1}

cc: @ablaom

[codecov-commenter]

Codecov Report

Merging #106 into master will increase coverage by 0.09%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #106      +/-   ##
==========================================
+ Coverage   96.87%   96.96%   +0.09%     
==========================================
  Files           2        2              
  Lines          32       33       +1     
==========================================
+ Hits           31       32       +1     
  Misses          1        1              

Impacted Files	Coverage Δ
src/scitype.jl	100.00% <100.00%> (ø)

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[tlienart]

Thanks that makes sense