Fix next and next2 buttons disabled if maxDate was set to the 1st millisecond of nextActiveStartDate or nextActiveStartDate2 respectively

Closes #485

Author: wojtekmaj

src/Calendar/Navigation.jsx

@@ -71,12 +71,12 @@ export default function Navigation({
     return minDate && minDate >= previousActiveEndDate;
   })();
 
-  const nextButtonDisabled = maxDate && maxDate <= nextActiveStartDate;
+  const nextButtonDisabled = maxDate && maxDate < nextActiveStartDate;
 
   const next2ButtonDisabled = (
     shouldShowPrevNext2Buttons
     && maxDate
-    && maxDate <= nextActiveStartDate2
+    && maxDate < nextActiveStartDate2
   );
 
   function onClickPrevious() {

src/Calendar/Navigation.spec.jsx

@@ -445,6 +445,42 @@ describe('Navigation', () => {
     expect(next2.prop('disabled')).toBeTruthy();
   });
 
+  it('does not disallow navigating to next month when maxDate is set to first day of the next month', () => {
+    const component = shallow(
+      <Navigation
+        {...defaultProps}
+        maxDate={new Date(2017, 1, 1)}
+        view="month"
+      />,
+    );
+
+    const arrows = component.find('button.react-calendar__navigation__arrow');
+
+    const next = arrows.at(2);
+    const next2 = arrows.at(3);
+
+    expect(next.prop('disabled')).toBeFalsy();
+    expect(next2.prop('disabled')).toBeTruthy();
+  });
+
+  it('does not disallow navigating to next year when maxDate is set to first day of the next year', () => {
+    const component = shallow(
+      <Navigation
+        {...defaultProps}
+        maxDate={new Date(2018, 0, 1)}
+        view="month"
+      />,
+    );
+
+    const arrows = component.find('button.react-calendar__navigation__arrow');
+
+    const next = arrows.at(2);
+    const next2 = arrows.at(3);
+
+    expect(next.prop('disabled')).toBeFalsy();
+    expect(next2.prop('disabled')).toBeFalsy();
+  });
+
   it('disallows navigating after dynamically set maxDate', () => {
     const component = shallow(
       <Navigation