Fix haddock comment

In 2da679f7, the CollectorData and CollectorMap types were
introduced. However, in the comment explaining those types,
the word "above" actually refered to a type introduced
later. Fix that.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

src/Ganeti/DataCollectors/Types.hs

@@ -135,7 +135,7 @@ instance JSON DCVersion where
     then Ok DCVerBuiltin else Ok . DCVersion $ fromJSString s
   readJSON v = fail $ "Invalid JSON value " ++ show v ++ " for type DCVersion"
 
--- | Type for the value field of the above map.
+-- | Type for the value field of the `CollectorMap` below.
 data CollectorData = CPULoadData (Seq.Seq (Integer, [Int]))
 
 -- | Type for the map storing the data of the statefull DataCollectors.