Use getDate instead of getDay (#8)

Date.prototype.getDay returns the day of the week whereas
Date.prototype.getDate returns the day of the month.

07-property-example.html

@@ -14,7 +14,7 @@
 // it formats a date and returns a <span> containing that formatted string
 function DateSpan(props) {
  var date = props.date,
- day = date.getDay(),
+ day = date.getDate(),
  month = date.getMonth() + 1,
  year = date.getFullYear()