minor #6820 Fixed the main index page redirections (javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Fixed the main index page redirections

I'm sorry but in a previous PR I configured these redirections wrongly. I've just tested this change locally and it works as expected. Thanks!

Commits
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47f1287 Fixed the main index page redirections

Author: xabbuh

_build/redirection_map

@@ -1,5 +1,5 @@
-/book/index /
-/cookbook/index /
+/book/index /index
+/cookbook/index /index
 /book/stable_api /contributing/code/bc
 /book/internals /reference/events
 /cookbook/console/sending_emails /cookbook/console/request_context