Fix twilight text selection

I'm not 100% on the color so please glance over this real quick.
The original twilight had both:
```css
pre[class*="language-"]::selection { /* Safari */
	background:hsl(200, 4%, 16%); /* #282A2B */
}
pre[class*="language-"]::selection { /* Firefox */
	background:hsl(200, 4%, 16%); /* #282A2B */
}
```
And:
```css
/* Text Selection colour */
::selection {
	background: hsla(0,0%,93%,0.15); /* #EDEDED */
}
::-moz-selection {
	background: hsla(0,0%,93%,0.15); /* #EDEDED */
}
```

I'm not sure which highlight was intended really. I went with the lighter:
```css
/* Text Selection colour */
pre[class*="language-"]::-moz-selection, pre[class*="language-"] ::-moz-selection,
code[class*="language-"]::-moz-selection, code[class*="language-"] ::-moz-selection {
	text-shadow: none;
	background: hsla(0,0%,93%,0.15); /* #EDEDED */
}

pre[class*="language-"]::selection, pre[class*="language-"] ::selection,
code[class*="language-"]::selection, code[class*="language-"] ::selection {
	text-shadow: none;
	background: hsla(0,0%,93%,0.15); /* #EDEDED */
}
```