aider: Add y-axis label "Percent correct" to the leaderboard chart.

# Aider chat conversation:

USER: add y-axis label "Percent correct"

ASSISTANT: ```diff
--- docs/leaderboard.md
+++ docs/leaderboard.md
@@ ... @@
 var leaderboardChart = new Chart(ctx, {
   type: 'bar',
   data: leaderboardData,
   options: {
     scales: {
       yAxes: [{
+        scaleLabel: {
+          display: true,
+          labelString: 'Percent correct'
+        },
         ticks: {
           beginAtZero: true
         }
       }]
     }
   }
 });
```

docs/leaderboard.md

@@ -65,6 +65,10 @@ it will work best with models that score well on the code editing benchmark.
       options: {
         scales: {
           yAxes: [{
+            scaleLabel: {
+              display: true,
+              labelString: 'Percent correct'
+            },
             ticks: {
               beginAtZero: true
             }