Make line-height for chapter greater than section

[JIghtuse]

Fixes #166

[azerupi]

You should modify the source files in src/theme/stylus and run cargo build --features="regenerate-css" instead of modifying the css file directly. Otherwise your change will be overwritten next time the css is regenerated :)

[JIghtuse]

@azerupi got it.
"regenerate-css" was failing on my machine due to missing stylus, so I've installed it and also some nib thing with npm. Now it builds fine, but throws away some stuff not related to line-heights. Should I amend this to include only relevant changes?

[azerupi]

Sorry for the delay!
The stuff that gets thrown away is probably a PR I accepted that modified the css instead of the stylus files. I'm going to copy that part and commit it properly.

Thanks!