Update redirects.csv

Had to add a redirect to the title case fix I did.

Author: strepanier03

docs/redirects.csv

@@ -878,4 +878,5 @@ https://help.expensify.com/articles/new-expensify/travel/Track-Travel-Analytics,
 https://help.expensify.com/articles/new-expensify/travel/Travel-Approval-Types,https://help.expensify.com/travel/hubs/
 https://help.expensify.com/articles/new-expensify/travel/Manage-Travel-Member-Roles,https://help.expensify.com/travel/hubs/
 https://help.expensify.com/articles/new-expensify/travel/Edit-or-cancel-travel-arrangements,https://help.expensify.com/travel/hubs/
-https://help.expensify.com/articles/expensify-classic/travel/Expensify-Travel-Tutorial,https://help.expensify.com/travel/hubs/
+https://help.expensify.com/articles/expensify-classic/travel/Expensify-Travel-Tutorial,https://help.expensify.com/travel/hubs/
+https://help.expensify.com/articles/travel/booking-travel/Book-A-Flight,https://help.expensify.com/articles/travel/booking-travel/Book-a-Flight