docs: change some references from http to https (#75)

Author: D3SOX

custom/config-vite.md

@@ -2,7 +2,7 @@
 
 <Environment type="node" />
 
-Slidev is powered by [Vite](http://vitejs.dev/) under the hood. This means you can leverage Vite's great plugin system to customize your slides even further.
+Slidev is powered by [Vite](https://vitejs.dev/) under the hood. This means you can leverage Vite's great plugin system to customize your slides even further.
 
 The `vite.config.ts` will be respected if you have one.
 

custom/directory-structure.md

@@ -115,7 +115,7 @@ import './code.css'
 import './layouts.css'
 ```
 
-Styles will be processed by [Windi CSS](http://windicss.org/) and [PostCSS](https://postcss.org/), so you can use css nesting and [at-directives](https://windicss.org/features/directives.html) out-of-box. For example:
+Styles will be processed by [Windi CSS](https://windicss.org/) and [PostCSS](https://postcss.org/), so you can use css nesting and [at-directives](https://windicss.org/features/directives.html) out-of-box. For example:
 
 ```less
 .slidev-layout {

guide/syntax.md

@@ -72,7 +72,7 @@ console.log('Hello, World!')
 //```
 ~~~
 
-We support [Prism](http://prismjs.com) and [Shiki](https://github.com./shikijs/shiki) as syntax highlighters. Refer to [the highlighters section](/custom/highlighters) for more details.
+We support [Prism](https://prismjs.com) and [Shiki](https://github.com./shikijs/shiki) as syntax highlighters. Refer to [the highlighters section](/custom/highlighters) for more details.
 
 ### Line Highlighting