[examples] use constants from src, not lib

Fixes #818.

examples/DateRangePickerWrapper.jsx

@@ -8,7 +8,7 @@ import DateRangePicker from '../src/components/DateRangePicker';
 
 import { DateRangePickerPhrases } from '../src/defaultPhrases';
 import DateRangePickerShape from '../src/shapes/DateRangePickerShape';
-import { START_DATE, END_DATE, HORIZONTAL_ORIENTATION, ANCHOR_LEFT } from '../constants';
+import { START_DATE, END_DATE, HORIZONTAL_ORIENTATION, ANCHOR_LEFT } from '../src/constants';
 import isInclusivelyAfterDay from '../src/utils/isInclusivelyAfterDay';
 
 const propTypes = {

examples/DayPickerRangeControllerWrapper.jsx

@@ -10,7 +10,7 @@ import DayPickerRangeController from '../src/components/DayPickerRangeController
 
 import ScrollableOrientationShape from '../src/shapes/ScrollableOrientationShape';
 
-import { START_DATE, END_DATE, HORIZONTAL_ORIENTATION } from '../constants';
+import { START_DATE, END_DATE, HORIZONTAL_ORIENTATION } from '../src/constants';
 import isInclusivelyAfterDay from '../src/utils/isInclusivelyAfterDay';
 
 const propTypes = forbidExtraProps({

examples/DayPickerSingleDateControllerWrapper.jsx

@@ -10,7 +10,7 @@ import DayPickerSingleDateController from '../src/components/DayPickerSingleDate
 
 import ScrollableOrientationShape from '../src/shapes/ScrollableOrientationShape';
 
-import { HORIZONTAL_ORIENTATION } from '../constants';
+import { HORIZONTAL_ORIENTATION } from '../src/constants';
 import isInclusivelyAfterDay from '../src/utils/isInclusivelyAfterDay';
 
 const propTypes = forbidExtraProps({

examples/SingleDatePickerWrapper.jsx

@@ -8,7 +8,7 @@ import SingleDatePicker from '../src/components/SingleDatePicker';
 
 import { SingleDatePickerPhrases } from '../src/defaultPhrases';
 import SingleDatePickerShape from '../src/shapes/SingleDatePickerShape';
-import { HORIZONTAL_ORIENTATION, ANCHOR_LEFT } from '../constants';
+import { HORIZONTAL_ORIENTATION, ANCHOR_LEFT } from '../src/constants';
 import isInclusivelyAfterDay from '../src/utils/isInclusivelyAfterDay';
 
 const propTypes = {