Skip writing about axes that we haven't touched

So currently, outputted code can look something like the following:

    nv.addGraph(function() {
        var chart = nv.models.lineChart();
        chart.xAxis
        chart.yAxis
            .tickFormat(d3.format(',.02f'));
        chart.showLegend(true);
        d3.select('#Priceovertime svg')
            .datum(data_Priceovertime)
            .transition().duration(500)
            .attr('width', 800)
.attr('height', 300)
            .call(chart);

Which is technically valid JS, but the `chart.xAxis` looks weird because we're basically invoking the attribute but not actually doing anything with it.  This is a pretty simple fix -- if there isn't anything we actually call on the axis, then we skip over it.

(BTW: also included in this was the previous slugify PR which you closed, but you closed the associated issue so I'm assuming you meant to hit merge?  If not, let me know.)