Fix react unique keys console warning

src/PointMap.js

@@ -135,8 +135,8 @@ class PointMap extends Component {
           <Typography gutterBottom variant="headline" component="h3">
             {name}
           </Typography>
-          { data.map(d => (
-            <div style={styles.val_div}>
+          { data.map((d, idx) => (
+            <div key={idx} style={styles.val_div}>
               <Typography variant="caption">
                 {d.h}
               </Typography>