message: Don't print a line for files that have no uncovered lines
diff: @@ -196,8 +196,10 @@ pub fn report_coverage(config: &Config, result: &TraceMap) {
  uncovered_lines.into_iter()
  .fold((vec![], vec![]), accumulate_lines);
  let (groups, _) = accumulate_lines((groups, last_group), u64::max_value());
  + if ! groups.is_empty() {
  println!("{}: {}", path.display(), groups.join(", "));
  }
  + }
  println!();
  }
  println!("Tested/Total Lines:");
  