In serialise function, the `strikeThrough` option is not possible to change via `nodeTypes`

[pradel]

Currently, there is no way to customise the strikeThrough name via the serialise function. The following code is not working:

serialize(v, {
  nodeTypes: {
    ...defaultNodeTypes,
    // not working
    delete_mark: 'underlined',
  },
});

This line needs to be changed https://github.com/hanford/remark-slate/blob/master/src/serialize.ts#L155.