Update part6d.md

Added a period at the end of sentence in exercise 6.22.

Author: cabbachew

src/content/6/en/part6d.md

@@ -389,7 +389,7 @@ Implement adding new anecdotes to the server using React Query. The application
 
 #### Exercise 6.22
 
-Implement voting for anecdotes using again the React Query. The application should automatically render the increased number of votes for the voted anecdote
+Implement voting for anecdotes using again the React Query. The application should automatically render the increased number of votes for the voted anecdote.
 
 </div>