SumBag: Fix typos in error messages and comments

src/Data/SumBag.hs

@@ -113,7 +113,7 @@ rotateSingleRight _ _ _ = error "rotateSingleRight called with empty left tree"
 
 rotateDoubleLeft :: Monoid a => Element a -> Tree a -> Tree a -> Tree a
 rotateDoubleLeft a x (Node _ c (Node _ b y1 y2) z) = node b (node a x y1) (node c y2 z)
-rotateDoubleLeft _ _ _ = error "rotateDoubleLeft called with too small left tree"
+rotateDoubleLeft _ _ _ = error "rotateDoubleLeft called with too small right tree"
 
 rotateDoubleRight :: Monoid a => Element a -> Tree a -> Tree a -> Tree a
 rotateDoubleRight c (Node _ a x (Node _ b y1 y2)) z = node b (node a x y1) (node c y2 z)
@@ -136,7 +136,7 @@ balance1 a left right
         sizeLL = size lleft
         sizeLR = size lright
     in if sizeLL < sizeLR then rotateSingleRight a left right else rotateDoubleRight a left right
-  -- No subtree is too heave, we can just form a new tree straight away
+  -- No subtree is too heavy, we can just form a new tree straight away
   | otherwise = node a left right
 
 addOnce :: Semigroup a => Element a -> Element a