Fix Markdown spec link (microsoft#41375)

Author: DanielRosenwasser

README.md

@@ -34,7 +34,7 @@ There are many ways to [contribute](https://github.com/microsoft/TypeScript/blob
 * Join the [#typescript](https://twitter.com/search?q=%23TypeScript) discussion on Twitter.
 * [Contribute bug fixes](https://github.com/microsoft/TypeScript/blob/master/CONTRIBUTING.md).
 * Read the archived language specification ([docx](https://github.com/microsoft/TypeScript/blob/master/doc/TypeScript%20Language%20Specification%20-%20ARCHIVED.docx?raw=true),
- [pdf](https://github.com/microsoft/TypeScript/blob/master/doc/TypeScript%20Language%20Specification%20-%20ARCHIVED.pdf?raw=true), [md](https://github.com/microsoft/TypeScript/blob/master/doc/spec-archived.md)).
+ [pdf](https://github.com/microsoft/TypeScript/blob/master/doc/TypeScript%20Language%20Specification%20-%20ARCHIVED.pdf?raw=true), [md](https://github.com/microsoft/TypeScript/blob/master/doc/spec-ARCHIVED.md)).
 
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