add type for pan field

dist/index.d.ts

@@ -14,7 +14,7 @@ declare abstract class ChartwerkPod<T extends TimeSerie, O extends Options> {
     protected zoom?: any;
     protected svg?: d3.Selection<SVGElement, unknown, null, undefined>;
     protected state: PodState<T, O>;
-    protected pan?: any;
+    protected pan?: d3.ZoomBehavior<Element, unknown>;
     protected clipPath?: any;
     protected isPanning: boolean;
     protected isBrushing: boolean;

src/index.ts

@@ -113,7 +113,7 @@ abstract class ChartwerkPod<T extends TimeSerie, O extends Options> {
   protected zoom?: any;
   protected svg?: d3.Selection<SVGElement, unknown, null, undefined>;
   protected state: PodState<T, O>;
-  protected pan?: any; // TODO: not any;
+  protected pan?: d3.ZoomBehavior<Element, unknown>;
   protected clipPath?: any;
   protected isPanning = false;
   protected isBrushing = false;