Ensure choropleths use the correct column for computing the scale. Resolves #4221

frontend/src/metabase/visualizations/components/ChoroplethMap.jsx

@@ -166,7 +166,7 @@ export default class ChoroplethMap extends Component {
             valuesMap[getRowKey(row)] = (valuesMap[getRowKey(row)] || 0) + getRowValue(row);
         }
 
-        var colorScale = d3.scale.quantize().domain(d3.extent(rows, d => d[1])).range(HEAT_MAP_COLORS);
+        var colorScale = d3.scale.quantize().domain(d3.extent(rows, getRowValue)).range(HEAT_MAP_COLORS);
 
         let legendColors = HEAT_MAP_COLORS.slice();
         let legendTitles = HEAT_MAP_COLORS.map((color, index) => {