title: Limit formatted Measurement to 2 digits
body: <p>I'd like to print a string based on a Measurement but limit it to 2 digits. I am using the <strong>MeasurementFormatter</strong> for this.</p>
  
  <pre><code>var beans:Measurement = Measurement(value: 20.22321, unit: UnitMass.milligrams) // "20.22321 mg"
  let formatter = MeasurementFormatter()
  formatter.numberFormatter.maximumFractionDigits = 2
  let label = formatter.string(from: beans) // 0 lb
  </code></pre>
  
  <p>I expected <code>20.22 mg</code> as a results, not <code>0 lb</code>. Where's my mistake?</p>