code: public IntStreamEx mapLast(IntUnaryOperator mapper) {
          return delegate(new PairSpliterator.PSOfInt((a, b) -> a, mapper, spliterator(), PairSpliterator.MODE_MAP_LAST));
      }
docs: Returns a stream where the last element is the replaced with the result
  of applying the given function while the other elements are left intact.
  
  <p>
  This is a <a href="package-summary.html#StreamOps">quasi-intermediate
  operation</a>.
  
  <p>
  The mapper function is called at most once. It could be not called at all
  if the stream is empty or there is short-circuiting operation downstream.
  
  @param mapper a
  <a href="package-summary.html#NonInterference">non-interfering
  </a>, <a href="package-summary.html#Statelessness">stateless</a>
  function to apply to the last element
  @return the new stream
  @since 0.4.1