Don't use moment-range overlaps method

The moment-range `overlaps` method doesn't consider ranges which 'touch' on equal start/end moments to be overlapping. This breaks highlighting and selection display across month boundaries.
Instead, explicitly test if the first range contains the start and end days of the second range.

src/DateRangePicker.jsx

@@ -452,21 +452,17 @@ const DateRangePicker = React.createClass({
     let monthEnd = monthDates.last().last();
     let monthRange = moment.range(monthStart, monthEnd);
 
-    if (moment.isMoment(value)) {
-      if (!monthRange.contains(value)) {
-        value = null;
-      }
-    } else if (isMomentRange(value)) {
-      if (!monthRange.overlaps(value)) {
-        value = null;
-      }
+    if (moment.isMoment(value) && !monthRange.contains(value)) {
+      value = null;
+    } else if (isMomentRange(value) && !(monthRange.contains(value.start) || monthRange.contains(value.end))) {
+      value = null;
     }
 
     if (!moment.isMoment(highlightedDate) || !monthRange.contains(highlightedDate)) {
       highlightedDate = null;
     }
 
-    if (!isMomentRange(highlightedRange) || !monthRange.overlaps(highlightedRange)) {
+    if (!isMomentRange(highlightedRange) || !(monthRange.contains(highlightedRange.start) || monthRange.contains(highlightedRange.end))) {
       highlightedRange = null;
     }