Make _.clone clone Date, RegExp, and Number  #1915

Fixes #1915 
> Looks like cloning the regexp fails to clone the flags (global, ignore case, multiline). Cloning these is not trivial. Should I still do that as part of this PR?

See [initObjectClone](https://github.com/lodash/lodash/blob/08b956cf884a5696f24284c9377cb4fa93c1294e/dist/lodash.js#L3095-L3137) for a reference *(ignore the typed array stuff)*.