correct i18n placeholder

src/app/components/home/_dialogs/user-activation/user-activation.component.html

@@ -6,7 +6,7 @@
            [formControl]="activationKeyFormControl" name="activation-key"
            aria-labelledby="activation-key-input-description"/>
     <mat-placeholder class="placeholder">{{ 'login.activation-key' | translate }}</mat-placeholder>
-    <mat-error *ngIf="activationKeyFormControl.hasError('required')">{{ 'login.activation-key-required' | translate }}</mat-error>
+    <mat-error *ngIf="activationKeyFormControl.hasError('required')">{{ 'user-activation.activation-key-required' | translate }}</mat-error>
   </mat-form-field>
 </form><div fxLayout="column" fxLayoutAlign="space-around">
   <button (click)="resetActivation()" mat-flat-button type="button"