message: fix: remove flock if it exists
diff: @@ -212,8 +212,12 @@ pub fn run_npm_install(dir: PathBuf) -> Result<(), failure::Error> {
  info!("skipping npm install because node_modules exists");
  }
  - flock.unlock()?;
  + // TODO(sven): figure out why the file doesn't exits in some cases? Even if
  + // the thread should have locked it.
  + if flock_path.exists() {
  fs::remove_file(&flock_path)?;
  + }
  + flock.unlock()?;
  Ok(())
  }
  