Add missing modifierKey properties to Options (#502)

* Add missing properties to Options

- Missing `modifierKey` to `PanOptions`
- Missing `wheelModifierKey` to `ZoomOptions`

* Update options.d.ts

Apply lint fix (remove trailing spaces).

Author: jbelien

types/options.d.ts

@@ -2,6 +2,7 @@ import { Chart, Color, Point } from 'chart.js';
 
 
 type Mode = 'x' | 'y' | 'xy';
+type Key = 'ctrl' | 'alt' | 'shift' | 'meta';
 
 export interface DragEffectOptions {
   borderColor?: Color;
@@ -48,6 +49,11 @@ export interface ZoomOptions {
    */
   threshold?: number;
 
+  /**
+   * Modifier key required for zooming with mouse
+   */
+  wheelModifierKey?: Key;
+
   /**
    * Function called while the user is zooming
    */
@@ -87,6 +93,11 @@ export interface PanOptions {
    */
   mode?: Mode | { (char: Chart): Mode };
 
+  /**
+   * Modifier key required for panning with mouse
+   */
+  modifierKey?: Key;
+
   overScaleMode?: Mode | { (char: Chart): Mode };
 
   /**