code: function buildScales(){
              xScale = d3Scale.scaleBand()
                  .domain(data.map(getKey))
                  .rangeRound([0, chartWidth])
                  .paddingInner(0);
  
              yScale = d3Scale.scaleLinear()
                  .domain([0, d3Array.max(data, getValue)])
                  .rangeRound([chartHeight, 0]);
          }
docs: Creates the x and y scales of the graph
  @private