function save(targets, originalDir, tempDir){
  let _path;
  for (target of targets) {

    _path = path.normalize(target.canonicalPath)
                .replace(originalDir, tempDir);

    fs.outputFileSync(_path, target.source);
  }
}
Save a set of instrumented files to a temporary directory.
@param  {Object[]} targets   array of targets generated by `assembleTargets`
@param  {[type]} originalDir absolute path to original contracts directory
@param  {[type]} tempDir     absolute path to temp contracts directory