title: How to set maximumFractionDigits in swift 3 with NumberFormatter()
body: <p>I've been reading the Apple Developer Documentation and it appears that it's not updated for the class <code>NumberFormatter</code>, they say it swapped from <code>NSNumberFormatter</code> to just <code>NumberFormatter</code>.</p>
  
  <p>I've found a few examples of functionalities of this class in Swift 3 but I couldn't find how to set the <code>maximumFractionDigits</code>.</p>
  
  <p>When I have a Double like this 0.123456789, I'd like to convert it into a String with just 4 fractional digits for example, like this 0.1234.</p>