fix bug in which axes are scaled only to first data set

app/assets/javascripts/monitoring/components/graph.vue

@@ -153,8 +153,9 @@
         const axisYScale = d3.scale.linear()
           .range([this.graphHeight - this.graphHeightOffset, 0]);
 
-        axisXScale.domain(d3.extent(this.timeSeries[0].values, d => d.time));
-        axisYScale.domain([0, d3.max(this.timeSeries[0].values.map(d => d.value))]);
+        const allValues = this.timeSeries.reduce((all, { values }) => all.concat(values), []);
+        axisXScale.domain(d3.extent(allValues, d => d.time));
+        axisYScale.domain([0, d3.max(allValues.map(d => d.value))]);
 
         const xAxis = d3.svg.axis()
           .scale(axisXScale)