title: Swift remove ONLY trailing spaces from string
body: <p>many examples in SO are fixing both sides, the leading and trailing. My request is only about the trailing. 
  My input text is: "   keep my left side  "
  Desired output: "   keep my left side"</p>
  
  <p>Of course this command will remove both ends:</p>
  
  <pre><code>let cleansed = messageText.trimmingCharacters(in: .whitespacesAndNewlines)
  </code></pre>
  
  <p>Which won't work for me. </p>
  
  <p>How can I do it?</p>