npm bower deprecation about bourbon

[tysongach]

👋 Hi!

Bower announced back in 2017 that they would keep maintaining it, but began recommending that folks use alternative package managers.

We don't have a dependency on Bower, so you won't see deprecation warnings when installing the Bourbon npm package. But it is probably a good time to remove the mention of Bower from our readme. We also have a bower.json config file, but I don't think we can remove that until we release 6.0, as it could break the dependency for people.

[tysongach]

I've opened two PRs to address this:

• #1066 removes the mention of using Bower from the readme
• #1067 removes the Bower config file; this PR can't be merged until we release the next major version, 6.0

[tysongach]

#1067 has been merged.