Build failure with GHC 8.10.4 and 8.8.4: "Could not deduce (MonadIO (ScottyT e m))"

Hi, I have a build failure with GHC 8.10.4 and 8.8.4:

```
Web/Scotty/Session.hs:46:19: error:
• Could not deduce (MonadIO (ScottyT e m))
arising from a use of ‘liftIO’
from the context: MonadIO m
bound by the type signature for:
createSessionManager :: forall (m :: * -> *) e a.
MonadIO m =>
ScottyT e m (ScottySM a)
at Web/Scotty/Session.hs:44:1-61
• In a stmt of a 'do' block:
storage <- liftIO $ atomically $ newTVar HM.empty
In the expression:
do storage <- liftIO $ atomically $ newTVar HM.empty
liftIO $ forkIO $ maintainSessions storage
return $ ScottySM storage
In an equation for ‘createSessionManager’:
createSessionManager
= do storage <- liftIO $ atomically $ newTVar HM.empty
liftIO $ forkIO $ maintainSessions storage
return $ ScottySM storage
|
46 | do storage <- liftIO $ atomically $ newTVar HM.empty
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```