`induction_elim` should read `cases_elim` at one point

[david-christiansen]

The induction_eliminator attribute registers an eliminator for use by the induction tactic.

attr ::= ...
| induction_eliminator

The induction_eliminator attribute registers an eliminator for use by the cases tactic.

attr ::= ...
| cases_eliminator

In what way is the content incorrect?

The second paragraph should use the right attribute name.