Delete return_to after sign in

[paulcsmith]

It seems like it should work so maybe it is an issue with Lucky

authentic/src/authentic.cr

Lines 63 to 64 in 0bceeb9

	return_to = action.session[:return_to]
	action.session.delete(:return_to)

Alternatively, it could be that it needs to delete a string or that it is not mutating the action