Fixed typo in docs where wrong headers are referenced

[acelaya]

Q	A
Documentation	yes
Bugfix	kind of
BC Break	no
New Feature	no
RFC	no
QA	no

Description

This fixes a typo in the docs, where the Access-Control-Allowed-Max-Age and Access-Control-Exposed-Headers headers are referenced, where it should be Access-Control-Max-Age and Access-Control-Expose-Headers.

It's just a typo in the docs, the code is using the proper values.

This is the same as #15, but pointing to the proper branch

[samsonasik]

@acelaya thank you 👍