message: add clearLabel to docs
diff: @@ -99,7 +99,8 @@ onChange | func | required | Callback firing when date accepted
  returnMoment | boolean | true | Will return moment object in onChange
  invalidLabel | string | 'Unknown' | Displayed string if date cant be parsed (or null)
  okLabel | string | 'OK' | The label for the ok button
  -cancelLabel | string | 'CANCEL' | The label for the cancel button
  +cancelLabel | string | 'Cancel' | The label for the cancel button
  +clearLabel | string | 'Clear' | The label for the clear button
  labelFunc | func | null | Allow to specify dynamic label for text field `labelFunc(date, invalidLabel)`
  renderDay | func | null | Allow to specify custom renderer for day `renderDay(date, selectedDate, dayInCurrentMonth)`
  leftArrowIcon | react node, string | 'keyboard_arrow_left'| Left arrow icon
  @@ -120,7 +121,8 @@ onChange | func | required | Callback firing when date accepted
  returnMoment | boolean | true | Will return moment object in onChange
  invalidLabel | string | 'Unknown' | Displayed string if date cant be parsed (or null)
  okLabel | string | 'OK' | The label for the ok button
  -cancelLabel | string | 'CANCEL' | The label for the cancel button
  +cancelLabel | string | 'Cancel' | The label for the cancel button
  +clearLabel | string | 'Clear' | The label for the clear button
  labelFunc | func | null | Allow to specify dynamic label for text field `labelFunc(date, invalidLabel)`
  ampm | boolean | true | 12h/24h view for hour selection clock
  keyboard | boolean | false | Allow to manual input date to the text field
  @@ -146,7 +148,8 @@ onChange | func | required | Callback firing when date accepted
  returnMoment | boolean | true | Will return moment object in onChangeg
  invalidLabel | string | 'Unknown' | Displayed string if date cant be parsed (or null)
  okLabel | string | 'OK' | The label for the ok button
  -cancelLabel | string | 'CANCEL' | The label for the cancel button
  +cancelLabel | string | 'Cancel' | The label for the cancel button
  +clearLabel | string | 'Clear' | The label for the clear button
  labelFunc | func | null | Allow to specify dynamic label for text field `labelFunc(date, invalidLabel)`
  renderDay | func | null | Allow to specify custom renderer for day `renderDay(date, selectedDate, dayInCurrentMonth)`
  leftArrowIcon | react node, string | 'keyboard_arrow_left'| Left arrow icon
  