Go back to taking the absolute value, even tho it’s wrong.

This is still a poor approximation to the edit distance, but it’s a
better one than `sum`, and it’s still very cheap.

src/Diffing.hs

@@ -99,5 +99,5 @@ diffFiles parser renderer sourceBlobs = do
 -- | The sum of the node count of the diff’s patches.
 diffCostWithCachedTermSizes :: Diff a Info -> Integer
 diffCostWithCachedTermSizes diff = case runFree diff of
-  Free (info :< _) -> sum (cost <$> info)
+  Free (info :< _) -> abs $ runBothWith (-) (cost <$> info)
   Pure patch -> sum (cost . extract <$> patch)