Reset this.state.modified on form submit

[notAro14]

Submiting did not make this.state.modified resetting to false again.

Issue

For example, when passing Prompt component (react-router-dom) like so

const MyForm = () => {
  const history = useHistory()

  const submitHandler = () => {
    const success = doSomethingWithFormItems()
    success && history.push('/somewhere/else')
  }

  return (
    <Formol onSubmit={submitHandler} extra={(state) => (<Prompt when={state.modified} />)}
      {/* ... */}
    </Formol>)
}

It will prompt the user a warning message to confirm the redirection after form submitting. This hangs the redirection waiting for the user confirmation.

But the confirmation is implicit as soon as he clicks the submit button. Therefore there is no need to let the form in a modified state when submiting was successful.

[coveralls]

Pull Request Test Coverage Report for Build 458

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 438:	0.0%
Covered Lines:	735
Relevant Lines:	735

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💛 - Coveralls

[notAro14]

Poke @cmigazzi @gentooboontoo