fix issue #338

Author: kinfkong

src/app/app.component.html

@@ -81,7 +81,7 @@
       <button mat-icon-button (click)="clearHistory()"
               *ngIf="currentInstance"
               [disabled]="!currentInstance"
-              matTooltip="{{currentInstance?'Clear all history':''}}">
+              matTooltip="{{currentInstance?'Clear All History':''}}">
         <i class="material-icons">clear_all</i>
       </button>