Upgraded cc and added parallel feature

[CGMossa]

Lovely package! I thought that I'd make this small PR that upgrades cc and adds a parallel feature, that cc provides.

I upgraded cc because I was getting a warning, and thought maybe it was dealt with already in cc.

Let me know if I can do more here.

[ChrisDenton]

Sorry this wasn't looked at in a long time!

The cc change has been superseded by 6e68d9c.

I don't think this crate should force the use of the parallel feature because some users may not want it. If users want to opt-in to the parallel feature they can do so by depending on cc themselves and adding the feature.

So I'm closing this but thanks for the PR regardless!