Add tests for `_.map`, `_.invoke`, `_.shuffle`, and `_.sortBy` for treating numbers as empty.
Update docs [ci skip]
Update Underscore license year [ci skip]
Simplify `_.chain`
Merge pull request #508 from d10/docs

Docs improvements. [ci skip]
Merge pull request #509 from d10/chain

Simplify `_.chain`.
Update link to curry post in readme. [ci skip]
Merge branch 'master' of github.com:lodash/lodash
Formalize all instances of `meta data` as `metadata` [ci skip]
Improve docs [ci skip]
Merge pull request #510 from d10/docs

More doc cleanup. [ci skip]
Merge branch 'master' of github.com:lodash/lodash
Ensure sparse arrays are treated as dense by `_.keys` and `_.keysIn` and ensure support for string objects in `_.keys` and `_.keysIn`.
Avoid formal param use in `_.difference`.
Fix perf regression in `_.intersection`.
Rebuild dist.
Add `_.intersection` test for working with only secondary arguments.
Cleanup test wording.
Tweak `_.union` tests.
Fix test title typos. [ci skip]