Fix typos

Found via `codespell -L shouldbe`

Author: kianmeng

src/Chapter4.hs

@@ -321,7 +321,7 @@ class Functor f => Applicative f where
 Wow, that's a lot going on again! Where did all these scary creatures
 come? But if we look closer, it all looks a bit familiar already.
 
-We now can spot straightaway, that similar to Functors, only types
+We now can spot straight away, that similar to Functors, only types
 with kind `* -> *` can have an Applicative instance (e.g. Maybe, and
 not 'Int' or 'Char'), as we see the same 'f a' argument in the
 methods' types.

test/Test/Chapter4.hs

@@ -20,7 +20,7 @@ chapter4normal :: Spec
 chapter4normal = describe "Chapter4Normal" $ do
     describe "Task2: Functor for Secret" $ do
         let trap = Trap "it's a trap"
-        it "doen't affect trap" $
+        it "doesn't affect trap" $
             fmap @(Secret String) @Bool not trap `shouldBe` trap
         it "change reward, same type" $
             fmap @(Secret String) @Bool not (Reward False) `shouldBe` Reward True