Make the tooltip animation snappier for line charts

When data is coming in live, the tooltip can get bogged down by updates
causing the tooltip to never make it under the mouse, which looks like
either lag or a bug.

ui/app/styles/charts/tooltip.scss

@@ -15,6 +15,10 @@
     pointer-events: none;
     z-index: $z-tooltip;
 
+    &.is-snappy {
+      transition: 0.2s top ease-out, 0.05s left ease-out;
+    }
+
     &::before {
       pointer-events: none;
       display: inline-block;

ui/app/templates/components/line-chart.hbs

@@ -16,7 +16,7 @@
   <g class="x-axis axis" transform="translate(0, {{xAxisOffset}})"></g>
   <g class="y-axis axis" transform="translate({{yAxisOffset}}, 0)"></g>
 </svg>
-<div class="chart-tooltip {{if isActive "active" "inactive"}}" style={{tooltipStyle}}>
+<div class="chart-tooltip is-snappy {{if isActive "active" "inactive"}}" style={{tooltipStyle}}>
   <ol>
     <p>
       <span class="label">