replaced a dead link (#300)

replaced url protocol of OOCSS from https to http

src/pages/introduction.mdx

@@ -19,8 +19,8 @@ This is also true for long-term projects with legacy code (read ["How to Scale a
 
 There are plenty of [methodologies](https://github.com/awesome-css-group/awesome-css#naming-conventions--methodologies-bulb) out there aiming to reduce the CSS footprint, organize cooperation among programmers and maintain large CSS codebases. This is obvious in large projects like Twitter, Facebook and [GitHub](http://markdotto.com/2014/07/23/githubs-css/#two-bundles), but other projects often grow into some “Huge CSS file” state pretty quickly.
 
-- [OOCSS](https://oocss.org/) — Separating container and content with CSS “objects”
-- [SMACSS](https://smacss.com/) — Style-guide to write your CSS with five categories for CSS rules
+- [OOCSS](http://oocss.org/) — Separating container and content with CSS “objects”
+- [SMACSS](http://smacss.com/) — Style-guide to write your CSS with five categories for CSS rules
 - [SUITCSS](https://suitcss.github.io/) — Structured class names and meaningful hyphens
 - [Atomic](https://acss.io/) — Breaking down styles into atomic, or indivisible, pieces