Incorrect DataFrame example in docstring

[skylarbpayne]

The comment in line 51 of https://github.com/JuliaStats/DataFrames.jl/blob/master/src/dataframe/dataframe.jl is incorrect. It fails with the following error:

julia> v = ["x","y","z"][rand(1:3, 10)]
10-element Array{String,1}:
 "x"
 "x"
 "x"
 "z"
 "y"
 "z"
 "y"
 "z"
 "x"
 "x"

julia> df1 = DataFrame(Any[[1:10], v, rand(10)], [:A, :B, :C])
ERROR: ArgumentError: All columns in a DataFrame must be the same length
 in DataFrames.DataFrame(::Array{Any,1}, ::DataFrames.Index) at /home/skpayne/.julia/v0.5/DataFrames/src/dataframe/dataframe.jl:86
 in DataFrames.DataFrame(::Array{Any,1}, ::Array{Symbol,1}) at /home/skpayne/.julia/v0.5/DataFrames/src/dataframe/dataframe.jl:107

[nalimilan]

Actually, the problem comes from a change in Julia's concatenation behavior. The new syntax is DataFrame(Any[collect(1:10), v, rand(10)], [:A, :B, :C]).