Remove scrollbars unless needed

Ananke has a very minimal design but code sections were including
horizontal and vertical scrollbars even when there is only a single line
of code. I feel that removing them unless necessary leads to a less
cluttered look with no downsides.

This also includes a rebuild of the production file as requested here:
https://github.com/budparr/gohugo-theme-ananke/pull/279#issuecomment-638253759

data/webpack_assets.json

 {
   "app": {
     "js": "js/app.3fc0f988d21662902933.js",
-    "css": "css/app.4fc0b62e4b82c997bb0041217cd6b979.css"
+    "css": "css/app.b37174ad47f1bff003551bf8ef2ab3dc.css"
   }
 }

src/css/_code.css

 pre, .pre  {
   overflow-x: auto;
   overflow-y: hidden;
-  overflow:   scroll;
 }