example code error for `heatmaps` in doc

[touchft]

@PlotlyJS v0.18.8

Original doc (wrong):

function heatmap2()
    trace = heatmap(
        x=["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"],
        y=["Morning", "Afternoon", "Evening"],
        z=rand(1:30, 5, 3) #  <---- Here error is!
    )
    plot(trace)
end
heatmap2()

Correct code:

function heatmap2()
    trace = heatmap(
        x=["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"],
        y=["Morning", "Afternoon", "Evening"],
        z=rand(1:30, 3,5)
    )
    plot(trace)
end
heatmap2()