Update challenge_6.md

Signed-off-by: Sreeja <sreejasaha.ece2019@nsec.ac.in>

Author: shivaylamba

Challenges/challenge_6.md

@@ -11,7 +11,7 @@ In the markdown file that was created in Challenge 5, edit the details as follow
 ---
 name: your_name
 github_user_name: YOUR-GITHUB-USERNAME
-url_of_github_isse: Link_of_the_github_issue_created_in_first_challenge
+url_of_github_issue: Link_of_the_github_issue_created_in_first_challenge
 ---
 ```
 3. After making this change create a commit with a proper commit message and push the changes