title: Sort a stream descending number
body: <p>I have a list that which looks like this: <code>[3 : [Reasonable product ], 5 : [Great ]]</code>
  I want to sort (using streams) this list by the number before <code>:</code>.
  The list it has to look like this:
  <code>[5 : [Great ], 3 : [Reasonable product ]]</code>
  My code looks like this:
  <code>return ratingsForProduct.stream().sorted().collect(Collectors.toList());</code>
  I don't know how to use lambda function or what I have to put as parameter to sorted().</p>