In indicator, do not ignore threshold with value 0

Author: antoinerg

src/traces/indicator/plot.js

@@ -324,7 +324,7 @@ function drawBulletGauge(gd, plotGroup, cd, opts) {
     }
     fgBullet.exit().remove();
 
-    var data = cd.filter(function() {return trace.gauge.threshold.value;});
+    var data = cd.filter(function() {return trace.gauge.threshold.value || trace.gauge.threshold.value === 0;});
     var threshold = bullet.selectAll('g.threshold-bullet').data(data);
     threshold.enter().append('g').classed('threshold-bullet', true).append('line');
     threshold.select('line')
@@ -497,7 +497,7 @@ function drawAngularGauge(gd, plotGroup, cd, opts) {
     // Draw threshold
     arcs = [];
     var v = trace.gauge.threshold.value;
-    if(v) {
+    if(v || v === 0) {
         arcs.push({
             range: [v, v],
             color: trace.gauge.threshold.color,