Adjust ST makeAndIncrement example type

`Int -> ST m Int []` is incompatible with previous examples which use `Integer`.

When using `Int` in the type of `makeAndIncrement`, you'll get something like this:
```
- + Errors (1)
 `-- ST.idr line 20 col 27:
     When checking right hand side of makeAndIncrement with expected type
             STrans m Int [] (\result => [])
     
     When checking an application of function Control.ST.>>=:
             Error in state transition: 
                     Operation has preconditions: [x ::: State Integer] 
                     States here are: [var ::: State Int] 
                     Operation has postconditions: \result => [x ::: State Integer] 
                     Required result states here are: st2_fn
```

docs/st/state.rst

@@ -594,7 +594,7 @@ That is, ``increment`` begins and ends with ``x`` in state ``State Integer``.
 
 .. code-block:: idris
 
-  makeAndIncrement : Int -> ST m Int []
+  makeAndIncrement : Integer -> ST m Integer []
 
 That is, ``makeAndIncrement`` begins and ends with no resources.