minor doc fix (#4296)
minor doc fix (#4296)

* minor doc fix

* minor doc fix

* fix problem with apex closure (#4292)

Co-authored-by: William Falcon <e5e1cb06e66b4dca47141118074351278caaa7fe@columbia.edu>

* minor doc fix

* minor doc fix

Co-authored-by: William Falcon <e5e1cb06e66b4dca47141118074351278caaa7fe@columbia.edu>
Co-authored-by: Adrian Wälchli <5b4e4cffa129a3d56e8f9fb9c37adfa57835aadb@gmail.com>
williamFalcon/pytorch-lightning,williamFalcon/pytorch-lightning