Doctest failures

There are a few doctest failures, probably due to printing changes between Julia versions. Also, doctest failures do not currently fail the documentation build.

┌ Error: doctest failure in ~/work/DocStringExtensions.jl/DocStringExtensions.jl/src/utilities.jl:221-245
│ 
│ ```jldoctest; setup = :(using DocStringExtensions)
│ julia> DocStringExtensions.find_tuples(Tuple{String,Number,Int})
│ 1-element Array{DataType,1}:
│  Tuple{String,Number,Int64}
│ 
│ julia> DocStringExtensions.find_tuples(Tuple{T} where T <: Integer)
│ 1-element Array{DataType,1}:
│  Tuple{T<:Integer}
│ 
│ julia> s = Union{
│          Tuple{Int64},
│          Tuple{U},
│          Tuple{T},
│          Tuple{Int64,T},
│          Tuple{Int64,T,U}
│        } where U where T;
│ 
│ julia> DocStringExtensions.find_tuples(s)
│ 5-element Array{DataType,1}:
│  Tuple{Int64}
│  Tuple{U}
│  Tuple{T}
│  Tuple{Int64,T}
│  Tuple{Int64,T,U}
│ ```
│ 
│ Subexpression:
│ 
│ DocStringExtensions.find_tuples(Tuple{String,Number,Int})
│ 
│ Evaluated output:
│ 
│ 1-element Vector{DataType}:
│  Tuple{String, Number, Int64}
│ 
│ Expected output:
│ 
│ 1-element Array{DataType,1}:
│  Tuple{String,Number,Int64}
│ 
│     Tuple{T<:Integer}
└ @ Documenter.DocTests ~/.julia/packages/Documenter/oBZFM/src/DocTests.jl:385
┌ Error: doctest failure in ~/work/DocStringExtensions.jl/DocStringExtensions.jl/src/utilities.jl:221-245
│ 
│ ```jldoctest; setup = :(using DocStringExtensions)
│ julia> DocStringExtensions.find_tuples(Tuple{String,Number,Int})
│ 1-element Array{DataType,1}:
│  Tuple{String,Number,Int64}
│ 
│ julia> DocStringExtensions.find_tuples(Tuple{T} where T <: Integer)
│ 1-element Array{DataType,1}:
│  Tuple{T<:Integer}
│ 
│ julia> s = Union{
│          Tuple{Int64},
│          Tuple{U},
│          Tuple{T},
│          Tuple{Int64,T},
│          Tuple{Int64,T,U}
│        } where U where T;
│ 
│ julia> DocStringExtensions.find_tuples(s)
│ 5-element Array{DataType,1}:
│  Tuple{Int64}
│  Tuple{U}
│  Tuple{T}
│  Tuple{Int64,T}
│  Tuple{Int64,T,U}
│ ```
│ 
│ Subexpression:
│ 
│ DocStringExtensions.find_tuples(s)
│ 
│ Evaluated output:
│ 
│ 5-element Vector{DataType}:
│  Tuple{Int64}
│  Tuple{U}
│  Tuple{T}
│  Tuple{Int64, T}
│  Tuple{Int64, T, U}
│ 
│ Expected output:
│ 
│ 5-element Array{DataType,1}:
│  Tuple{Int64}
│  Tuple{U}
│  Tuple{T}
│  Tuple{Int64,T}
│  Tuple{Int64,T,U}
│ 
│   diff =
│    5-element Array{DataType,1}:
│     Vector{DataType}:
│     Tuple{Int64}
│     Tuple{U}
│     Tuple{T}
│     Tuple{Int64,T}
│     Tuple{Int64,T,U}Tuple{Int64, T}
│     Tuple{Int64, T, U}
└ @ Documenter.DocTests ~/.julia/packages/Documenter/oBZFM/src/DocTests.jl:385

Read src/utilities.jl:221-245 and inspect the reported doctest output across the relevant Julia version. Run the documentation build to reproduce the failures, then verify that the expected output is current and that a doctest failure causes the build to fail.