Update datepicker_example_1.txt

Just like in `components/date_picker/readme.md`, you need to add 1 to `
value.getMonth()`

docs/app/components/layout/main/modules/examples/datepicker_example_1.txt

@@ -30,7 +30,7 @@ class DatePickerTest extends React.Component {
         <DatePicker
           label='Formatted Date'
           autoOk
-          inputFormat={(value) => `${value.getDate()}/${value.getMonth()}/${value.getFullYear()}`}
+          inputFormat={(value) => `${value.getDate()}/${value.getMonth() + 1}/${value.getFullYear()}`}
           onChange={this.handleChange.bind(this, 'date3')}
           value={this.state.date3}
         />