Merge pull request #3961 from mempool/mononaut/fix-difficulty-chart

Fix difficulty chart off-by-one bug

frontend/src/app/components/hashrate-chart/hashrate-chart.component.ts

@@ -130,6 +130,7 @@ export class HashrateChartComponent implements OnInit {
                 });
                 ++hashIndex;
               }
+              diffIndex++;
               break;
             }