message: Simpler deep partial type
diff: @@ -3,11 +3,7 @@ import { isArray } from 'vega-util';
  /**
  * From Vega-Lite
  */
  -export type DeepPartial<T> = {
  - [P in keyof T]?: T[P] extends Array<infer U>
  - ? Array<DeepPartial<U>>
  - : T[P] extends ReadonlyArray<infer V> ? ReadonlyArray<DeepPartial<V>> : DeepPartial<T[P]>
  -};
  +export type DeepPartial<T> = { [P in keyof T]?: DeepPartial<T[P]> };
  export function mergeDeep<T>(dest: T, ...src: Array<DeepPartial<T>>): T {
  for (const s of src) {
  