respect array type (JuliaArrays#32)

Author: Pietro Vertechi

src/collect.jl

@@ -107,7 +107,7 @@ widenfieldarrays(dest::AbstractArray, i, el) = widenarray(dest, i, el)
 
 function widenarray(dest::AbstractArray{T}, i, el::S) where {S, T}
     S <: T && return dest
-    new = Array{promote_type(S, T)}(undef, length(dest))
+    new = similar(dest, promote_type(S, T), length(dest))
     copyto!(new, 1, dest, 1, i-1)
     new
 end