Fixed doc for framework.session.cookie_lifetime refrence.
bug #3475 Fixed doc for framework.session.cookie_lifetime refrence. (tyomo4ka)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #3475).

Discussion
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Fixed doc for framework.session.cookie_lifetime refrence.

| Q           | A
| ------------ | ---
| Doc fix? | yes
| New docs? | no
| Applies to | 2.3+
| Fixed tickets |

Commits
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39a65e1 Fixed doc for framework.session.cookie_lifetime refrence.