Update react-flatpickr with flatpickr's new exports

It switched to a default export that contains nested-nested types.

types/react-flatpickr/index.d.ts

@@ -5,12 +5,12 @@
 // TypeScript Version: 2.6
 
 import { Component } from 'react';
-import { Options } from 'flatpickr';
+import flatpickr from 'flatpickr';
 
 export interface DateTimePickerProps {
     defaultValue?: string;
-    options?: Options.Options;
-    onChange?: Options.Hook;
+    options?: flatpickr.Options.Options;
+    onChange?: flatpickr.Options.Hook;
     value?: string;
 }
 

types/react-flatpickr/react-flatpickr-tests.tsx

@@ -1,4 +1,4 @@
-import { Instance } from 'flatpickr';
+import flatpickr from 'flatpickr';
 import * as React from 'react';
 import DatePicker from 'react-flatpickr';
 
@@ -12,7 +12,7 @@ const options = {
 const optionsElement = <DatePicker options={ options }/>;
 
 const onChange = (
-    selectedDates: Date[], dateStr: string, instance: Instance,
+    selectedDates: Date[], dateStr: string, instance: flatpickr.Instance,
     elem: HTMLElement
 ) => null;
 const onChangeElement = <DatePicker onChange={ onChange }/>;