Update to header line heights

Formula: `[font-size] * 1.5 = [perfect line-height]`
Example: `46px * 1.5 = 69px`

*Implemented in the file change.*

I found out about this via [this presentation](https://speakerdeck.com/sachag/design-by-the-numbers?slide=5). I checked it out and it worked quite well. Worth implementing or at least looking at.