code: function trimNested(previous, current, opts) {
      // bail early if we want to keep nested dependencies
      if (opts.keepNested) {
          return current;
      }
  
      // purposes find patches from to
      // apply TO current FROM previous
      var patches = jsonDiff.diff(current, previous);
  
      if (!patches) {
          return current;
      }
  
      patches = removeTopLevelPatches(patches);
  
      if (patches.dependencies) {
          Object.keys(patches.dependencies)
              .forEach(function (key) {
                  current.dependencies[key] =
                      previous.dependencies[key];
              });
      }
  
      return current;
  }
docs: /*  var patches = diff(current, previous)
  
  for each NESTED (depth >=1) patch, apply it to current.
  
  Write new current into disk at dirname/npm-shrinkwrap.json