Deprecated doc for construction of DefaultDict

[scls19fr]

Hello,

I noticed in doc the following construction of DefaultDict

https://github.com/JuliaCollections/DataStructures.jl/blame/c31f17f0d0dead44ae7766b36fd880dcae666a9d/doc/src/default_dict.md#L18

but this kind of construction is deprecated so it shouldn't be in doc

julia> DefaultDict(String, Int, 0)
WARNING: DefaultDict(::Type{K}, ::Type{V}, default) where {K, V} is deprecated, use DefaultDict{K, V}(default) instead.
Stacktrace:
 [1] depwarn(::String, ::Symbol) at .\deprecated.jl:70
 [2] DataStructures.DefaultDict(::Type{String}, ::Type{Int64}, ::Int64) at .\deprecated.jl:57
 [3] eval(::Module, ::Any) at .\boot.jl:235
 [4] eval_user_input(::Any, ::Base.REPL.REPLBackend) at .\REPL.jl:66
 [5] macro expansion at .\REPL.jl:97 [inlined]
 [6] (::Base.REPL.##1#2{Base.REPL.REPLBackend})() at .\event.jl:73
while loading no file, in expression starting on line 0
DataStructures.DefaultDict{String,Int64,Int64} with 0 entries

julia> DefaultDict{String, Int}(0)
DataStructures.DefaultDict{String,Int64,Int64} with 0 entries

This issue is comparable to #340

Kind regards