message: output: sort output paths
  With a `HashMap`, the output order is undefined. Instead, use a
  `BTreeMap` and keep the output order stable.
diff: @@ -19,7 +19,7 @@ use std::io::{Error, ErrorKind};
  use std::ffi::CString;
  use std::path::{Path, PathBuf};
  use std::process::Command;
  -use std::collections::HashMap;
  +use std::collections::{BTreeMap, HashMap};
  use nix::Error as NixErr;
  use nix::unistd::*;
  use nix::libc::pid_t;
  @@ -202,7 +202,7 @@ pub fn report_coverage(config: &Config, result: &[TracerData]) {
  println!("");
  }
  // Hash map of files with the value (lines covered, total lines)
  - let mut file_map: HashMap<&Path, (u64, u64)> = HashMap::new();
  + let mut file_map: BTreeMap<&Path, (u64, u64)> = BTreeMap::new();
  for r in result.iter() {
  if file_map.contains_key(r.path.as_path()) {
  if let Some(v) = file_map.get_mut(r.path.as_path()) {
  