url double-quote argument

[jamesdbrock]

url() property needs double-quotes around its argument to work with data urls.

https://github.com/lumihq/purescript-react-basic-emotion/blob/be154d690292054393e71a0ede8d29beb4dce671/src/React/Basic/Emotion.purs#L211

[jamesdbrock]

Actually the quotes can be double or single https://www.w3.org/TR/CSS2/syndata.html#uri