title: "Warning: Failed prop type" When using react-datepikcer with redux-form
body: <p>I'm using "react-datepicker" alongside "redux-form", and I keep getting this error in the console ...</p>
  
  <pre><code>Warning: Failed prop type: Invalid prop `selected` of type `String` supplied to `DatePicker`, expected instance of `Date`.
  </code></pre>
  
  <p>The new version of "react-datepicker" is not using "moment()" so the solutions I found doesn't work.</p>
  
  <p>Here's how my form component looks like ...</p>
  
  <pre><code>import React, { Component } from "react";
  import { compose } from "redux";
  import { connect } from "react-redux";
  import { reduxForm, Field } from "redux-form";
  import DateInput from "../../form/DateInput";
  import { subDays } from "date-fns";
  import {
      combineValidators,
      isRequired
  } from "revalidate";
  
  class SignUpForm extends Component {
      onFormSubmit = values =&gt; {
          console.log(values);
      };
  
      render() {
          const { invalid, submitting, pristine } = this.props;
          return (
              &lt;form onSubmit={this.props.handleSubmit(this.onFormSubmit)}&gt;
                  &lt;Field
                      name="birthdate"
                      component={DateInput}
                      label="Birth Date"
                      dateFormat="yyyy-MM-dd"
                      showMonthDropdown
                      showYearDropdown
                      dropdownMode="select"
                      maxDate={subDays(new Date(), 366 * 18)}
                      showDisabledMonthNavigation
                  /&gt;
  
                  &lt;Button
                      disabled={invalid || submitting || pristine}
                      type="submit"
                      size="big"
                      theme="black"
                  &gt;
                      Sign In
                  &lt;/Button&gt;
              &lt;/form&gt;
          );
      }
  }
  
  const validate = combineValidators({
      birthdate: isRequired({ message: "Please choose your date of birth." })
  });
  
  export default compose(
      connect(
          null,
          actions
      ),
      reduxForm({ form: "signupForm", enableReinitialize: true, validate })
  )(SignUpForm);
  </code></pre>
  
  <p>And here's how the "DateInput" component looks like ...</p>
  
  <pre><code>import React from "react";
  import DatePicker from "react-datepicker";
  import "react-datepicker/dist/react-datepicker.css";
  
  const DateInput = ({
      input: { value, onChange, ...restInput },
      label,
      meta: { touched, error, dirty },
      ...props
  }) =&gt; {
      let groupClasses = touched &amp;&amp; !!error ? "input-group error" : "input-group";
  
      return (
          &lt;div className={groupClasses}&gt;
              &lt;DatePicker
                  {...props}
                  selected={value ? value : null}
                  onChange={onChange}
                  {...restInput}
              /&gt;
              {touched &amp;&amp; !!error &amp;&amp; &lt;span className="error"&gt;{error}&lt;/span&gt;}
          &lt;/div&gt;
      );
  };
  
  export default DateInput;
  </code></pre>
  
  <p>Any help would be appreciated.</p>