Fix redundant renders on TimeSince component

Author: benvinegar

src/sentry/static/sentry/app/components/timeSince.jsx

@@ -1,7 +1,12 @@
 import React from "react";
 import moment from "moment";
+import PureRenderMixin from 'react-addons-pure-render-mixin';
 
 var TimeSince = React.createClass({
+  mixins: [
+    PureRenderMixin
+  ],
+
   propTypes: {
     date: React.PropTypes.any.isRequired,
     suffix: React.PropTypes.string
@@ -31,10 +36,6 @@ var TimeSince = React.createClass({
     this.forceUpdate();
   },
 
-  shouldComponentUpdate(nextProps, nextState) {
-    return this.props.date !== nextProps.date;
-  },
-
   render() {
     var date = this.props.date;