v2.4.0

Features:

• Allow dom element to be passed as a custom prop without having to pass a domElementGetter (#30)
• singleSpaReact({...}) can now be used to create parcels (#30)

Maintenance:

• Created tests for single-spa-react
• Created a travis-ci.yml file and connected this repo to travis. See https://travis-ci.org/CanopyTax/single-spa-react