NPM Release v2.6.0

Fix Type Error when null is passed to deepKeys (#26)

* fix: resolve "TypeError: Cannot convert undefined or null to object"

Initially reported in https://github.com/mrodrig/json-2-csv/issues/222
This issue appears when a `null` value is passed for key enumeration because technically `null` is an object, but doesn't have keys. This commit fixes the issue by adding a null check to prevent the type error.

* chore(deps): npm audit fix

* chore(rel): 2.6.0