fix: link on markdown

When clicking the link from the full stack open website, (section 6.19. -6.21) the link directs me to https://fullstackopen.com/en/part6/(https://github.com/fullstack-hy2020/query-anecdotes).
I believe this is happening because in the markdown, the link is wrapped in double parentheses [this project]((linkhere)).

I have removed the double parentheses to resolve this issue.

Author: Dezzep

src/content/6/en/part6d.md

@@ -351,7 +351,7 @@ Most React applications need not only a way to temporarily store the served data
 
 ### Exercises 6.19.-6.21.
 
-Now let's make a new version of the anecdote application that uses the React Query library. Take [this project]((https://github.com/fullstack-hy2020/query-anecdotes)) as your starting point. The project has a ready-installed JSON Server, the operation of which has been slightly modified. Start the server with <i>npm run server</i>.
+Now let's make a new version of the anecdote application that uses the React Query library. Take [this project](https://github.com/fullstack-hy2020/query-anecdotes) as your starting point. The project has a ready-installed JSON Server, the operation of which has been slightly modified. Start the server with <i>npm run server</i>.
 
 #### Exercise 6.19