Update avatar image file extension

_config.yml

@@ -17,7 +17,7 @@ description: Junior CS Student at NYU
 # on the web). Replace "weekly" by the name of your own repository.
 # It should be "USER_NAME-weekly" in which USER_NAME is replaced by your actual
 # user name for GitHub.
-avatar: /wwwld1-weekly/images/avatar.png 
+avatar: /wwwld1-weekly/images/avatar.jpg 
 # fallback text in case image is not served and/or for screen readers
 avatar_alt_text: My Avatar
 # use this separator in your blogs to indicate where the abbreviated part ends and