Use pre instead of pre-line for code whitespace.

[mbrandonw]

This fixes the issue I filed #129

I think you want to use white-space: pre here in order to preserve spaces. pre-line will collapse the spaces:

Sequences of whitespace will collapse into a single whitespace. Text will wrap when necessary, and on line breaks

Another option is pre-wrap if you want long lines to wrap.

[mattt]

This looks great, @mbrandonw. Thank you for submitting this PR and for your patience as I ramp back up to working on swift-doc on a more regular basis. I look forward to cutting a new release by Friday with this fix and a whole raft of improvements.

[mbrandonw]

@mattt that is awesome to hear and no worries! really excited for the future of this project and we will be adding it to TCA shortly!