title: DateFormatter's returns nil for specific date strings without time in Swift
body: <p>I really don't get what is happening with this code, I'm trying to convert a string to date. What I don't understand is that the conversion works for most of the dates, but doesn't work specially for only 2 dates.</p>
  
  <pre><code>let dateFormatter = NSDateFormatter()
  dateFormatter.locale = NSLocale(localeIdentifier: "es")
  dateFormatter.dateFormat = "dd 'de' MMMM"
  
  dateFormatter.dateFromString("1 de octubre")
  dateFormatter.dateFromString("2 de octubre")
  dateFormatter.dateFromString("3 de octubre")
  dateFormatter.dateFromString("4 de octubre")
  dateFormatter.dateFromString("5 de octubre")
  dateFormatter.dateFromString("6 de octubre")
  dateFormatter.dateFromString("7 de octubre")
  dateFormatter.dateFromString("8 de octubre")
  dateFormatter.dateFromString("9 de octubre")
  dateFormatter.dateFromString("10 de octubre")
  dateFormatter.dateFromString("11 de octubre")
  dateFormatter.dateFromString("12 de octubre")
  dateFormatter.dateFromString("13 de octubre")
  dateFormatter.dateFromString("14 de octubre")
  dateFormatter.dateFromString("15 de octubre")
  dateFormatter.dateFromString("16 de octubre")
  dateFormatter.dateFromString("17 de octubre")
  dateFormatter.dateFromString("18 de octubre")
  dateFormatter.dateFromString("19 de octubre")
  dateFormatter.dateFromString("20 de octubre")
  dateFormatter.dateFromString("21 de octubre")
  dateFormatter.dateFromString("22 de octubre")
  dateFormatter.dateFromString("23 de octubre")
  dateFormatter.dateFromString("24 de octubre")
  dateFormatter.dateFromString("25 de octubre")
  dateFormatter.dateFromString("26 de octubre")
  dateFormatter.dateFromString("27 de octubre")
  dateFormatter.dateFromString("28 de octubre")
  dateFormatter.dateFromString("29 de octubre")
  dateFormatter.dateFromString("30 de octubre")
  </code></pre>
  
  <p>I made this code to try out in Playground, but it reproduces some dates I'm getting in my production code. Take a look in the output that this code produces:</p>
  
  <p><a href="https://i.stack.imgur.com/GGSO5.png" rel="noreferrer"><img src="https://i.stack.imgur.com/GGSO5.png" alt="Playground output"></a></p>
  
  <p>As you can see in the image, it doesn't work for October 8 and 15. Works for all the others. I also tried August and September, and in those months all days work. I also tried to put the dates in Portuguese in pt-br locale, and also doesn't work for October 8 and 15. Is it explainable?</p>
  
  <hr>
  
  <p>Update: @zneak code produces the following output for me:</p>
  
  <p><a href="https://i.stack.imgur.com/WavMd.png" rel="noreferrer"><img src="https://i.stack.imgur.com/WavMd.png" alt="output"></a></p>
  
  <p>In other words, stopped running October 8.</p>