Fix hook name in deprecations.rst
Fix hook name in deprecations.rst

As mentioned in https://github.com/pytest-dev/pytest/issues/4128#issuecomment-430690498
markshao/pytest,pytest-dev/pytest,pfctdayelise/pytest,Akasurde/pytest,tomviner/pytest,The-Compiler/pytest,tomviner/pytest,alfredodeza/pytest,nicoddemus/pytest,txomon/pytest,hackebrot/pytest,RonnyPfannschmidt/pytest,The-Compiler/pytest,nicoddemus/pytest