Activate `systemvars` to load all system and react .env variables

See #21

Updated babel presets and deps

Use same babel preset as CRA. (#13)

* Use same babel preset as CRA.

* Updated dependancies to babel 7.

* Replaced babel plugins with preset.

* Fix incorrect preset name.

* Fix preset name.

Enchamncements

Solves #5
Fixes #6

v2.2.0

Added replace output mode. Resolves #4.

v2.1.0

Fixes #1