Use lodash for deep cloning.

This way Date, Regexp and other non-plain objects
are preserved while copying.

Fixes #139.
Issue #139: use a different method for cloneDeep.

Fixes #139.
Issue #139: make sure `cloneDeep` signature doesn't change
Merge pull request #141 from diversario/fix/i139-regexp-date-corruption

Use lodash for deep cloning.