Fix(challenges): scroll instruction panel to top between challenges

closes #9361

common/app/routes/challenges/components/classic/Side-Panel.jsx

@@ -1,4 +1,5 @@
 import React, { PropTypes } from 'react';
+import ReactDom from 'react-dom';
 import { createSelector } from 'reselect';
 import { connect } from 'react-redux';
 
@@ -75,6 +76,12 @@ export class SidePanel extends PureComponent {
     });
   }
 
+  componentWillReceiveProps(nextProps) {
+    if (this.props.title !== nextProps.title) {
+      ReactDom.findDOMNode(this).scrollTop = 0;
+    }
+  }
+
   render() {
     const {
       title,