fix: use commonjs date-fns imports for rollup

Author: Matt Lewis

src/components/month/calendarMonthView.component.ts

@@ -11,7 +11,6 @@ import {
   LOCALE_ID,
   Inject
 } from '@angular/core';
-import * as isSameDay from 'date-fns/is_same_day';
 import {
   CalendarEvent,
   WeekDay,
@@ -23,6 +22,9 @@ import {
 import { Subject } from 'rxjs/Subject';
 import { Subscription } from 'rxjs/Subscription';
 
+declare const require: any;
+const isSameDay: any = require('date-fns/is_same_day');
+
 @Component({
   selector: 'mwl-calendar-month-view',
   changeDetection: ChangeDetectionStrategy.OnPush,

src/providers/calendarNativeDateFormatter.provider.ts

@@ -1,6 +1,8 @@
-import * as getISOWeek from 'date-fns/get_iso_week';
 import { CalendarDateFormatterInterface, DateFormatterParams } from './../interfaces/calendarDateFormatter.interface';
 
+declare const require: any;
+const getISOWeek: any = require('date-fns/get_iso_week');
+
 export class CalendarNativeDateFormatter implements CalendarDateFormatterInterface {
 
   public monthViewColumnHeader({date, locale}: DateFormatterParams): string {