message: addSyncMapFilter/initial: pass correct since value
  according to the typings, initial() should receive
  `since` with type `number | undefined` as it's 3rd
  parameter, but it actually receives a value of the
  `action.since` which type is
  `{ id: ID, time: number } | undefined`.
diff: @@ -188,14 +188,14 @@ export function addSyncMapFilter(server, plural, operations) {
  }
  },
  async load(ctx, action, meta) {
  + let since = action.since ? action.since.time : 0
  let data = await operations.initial(
  ctx,
  action.filter,
  - action.since,
  + since,
  action,
  meta
  )
  - let since = action.since ? action.since.time : 0
  await Promise.all(
  data.map(async i => {
  await server.subscribe(ctx.nodeId, `${plural}/${i.id}`)
  