doc: replace PrismJS with highlight.js

Author: SharzyL

README.md

@@ -7,7 +7,7 @@ This is a pastebin that can be deployed on Cloudflare workers. Try it on [shz.al
 **Features**:
 
 1. Share your paste with as short as 4 characters, or even customized URL.
-1. **Syntax highlighting** powered by PrismJS
+1. **Syntax highlighting** powered by highlight.js.
 1. Client-side encryption
 1. Render **markdown** file as HTML
 1. URL shortener