Added hover color variable and fixed the vertical alignment of the hamburger box

[jaclyntan]

I added a new color variable to hamburgers.scss called $hamburger-layer-hover-color to make it easier to change colours on hover.

I also added vertical-align: middle; to .hamburger-box so the burger is always properly centered inside .hamburger

I have used your work on a number of projects and really appreciate your effort on this!! Thank you for your awesome work.

[hepifish]

Hi there @jaclyntan,

I've also been looking over this feature. I know you posted the PR some time ago, but you should check the mobile version, it's not working really well (the hover color remains after the button is pressed, which is not the desired solution). I encountered the same issue and I was curious if your solution works, but seems to be the same issue, sadly.