fix minDate/maxDate fallback

Author: mkg0

src/components/Calendar.js

@@ -162,8 +162,8 @@ class Calendar extends PureComponent {
   }
   renderMonthAndYear(focusedDate, changeShownDate, props) {
     const { showMonthArrow, locale, minDate, maxDate, showMonthAndYearPickers } = props;
-    const upperYearLimit = maxDate.getFullYear();
-    const lowerYearLimit = minDate.getFullYear();
+    const upperYearLimit = (maxDate || Calendar.defaultProps.maxDate).getFullYear();
+    const lowerYearLimit = (minDate || Calendar.defaultProps.minDate).getFullYear();
     const styles = this.styles;
     return (
       <div onMouseUp={e => e.stopPropagation()} className={styles.monthAndYearWrapper}>