Accidentally isolating DOM source

[b123400]

When isolating form like this:

import { isolate } from 'cyclic-form';

isolate(stateLens)(Form)({
  DOM,
  state,
});

It seems Cycle.js automatically assumes all unspecified sources should be isolated with a default scope, which means the above code is equivalent to

import isolate from '@cycle/isolate';

isolate(Form, { state: stateLens, DOM: 'cycle1' /* the default scope name */ })({
  DOM,
  state,
})

This behaviour breaks the submit button because it cannot interfere with form's `submit event.
Something like this is needed, but the current API isn't possible:

import isolate from '@cycle/isolate';

isolate(Form, { state: stateLens, DOM: null /* explicitly prevent isolation */ })({
  DOM,
  state,
})