CSS adds too much space between lines in <pre>s

[jadrian]

On https://flyingzumwalt.gitbooks.io/decentralized-web-primer/content/install-ipfs/lessons/initialize-repository.html , there are two separate issues with pre blocks:

• There's a lot of space between lines in multi-line blocks. This makes the readme, for example, render really ugly.
• The preformatted text is larger within the note box ("... you will get an error message like...") than it is elsewhere, though regular text in the note box is the same size as text elsewhere.