Fix ternary.sum relayout recalculation

[Lexachoc]

Closes #8127

Ensure changes to layout.ternary.sum trigger recalculation of ternary trace data, preventing stale calcdata after Plotly.relayout.

Reproduce with devtools

Open:

http://localhost:3000/devtools/test_dashboard/index.html

Then run in the console:

Plotly.newPlot(gd, [{
    type: 'scatterternary',
    mode: 'markers',
    a: [0.2],
    b: [0.3],
    marker: {size: 16},
    hovertemplate:
        'a=%{a}<br>' +
        'b=%{b}<br>' +
        'c=%{c}<extra></extra>'
}], {
    ternary: {
        sum: 1
    }
});

Then:

Plotly.relayout(gd, {
    'ternary.sum': 100
});

Or see the CodePen: https://codepen.io/Lexachoc/pen/EaWEpLx