Add zoom_speed to LGraphCanvas type def (#83)

public/litegraph.d.ts

@@ -1316,6 +1316,7 @@ export declare class LGraphCanvas {
     visible_links: LLink[];
     visible_nodes: LGraphNode[];
     zoom_modify_alpha: boolean;
+    zoom_speed: number;
     //mouse in canvas coordinates, where 0,0 is the top-left corner of the blue rectangle
     mouse: Vector2;
     //mouse in graph coordinates, where 0,0 is the top-left corner of the blue rectangle