Sorting error using examples from docs

[IanButterworth]

For both v0.19.3 and master on Julia v1.2:

using DataFrames, CSV
iris = CSV.read(joinpath(dirname(pathof(DataFrames)), "../docs/src/assets/iris.csv"))
sort!(iris)

ERROR: LoadError: ArgumentError: CSV.Column is read-only; to get a mutable vector, do `copy(col)` or to make all columns mutable do `CSV.read(file; copycols=true)` or `CSV.File(file) |> DataFrame`
Stacktrace:
 [1] setindex!(::CSV.Column{Float64,Float64}, ::Float64, ::Int64) at /home/ian/.julia/packages/CSV/KgT4M/src/tables.jl:26
 [2] permute!!(::CSV.Column{Float64,Float64}, ::Array{Int64,1}) at ./combinatorics.jl:107