fix findParam to make usage of Maybe reasonable

ch08.md

@@ -455,14 +455,14 @@ const toPairs = compose(map(split('=')), split('&'));
 // params :: String -> [[String]]
 const params = compose(toPairs, last, split('?'));
 
-// findParam :: String -> IO Maybe [[String]]
-const findParam = key => map(compose(Maybe.of, filter(compose(eq(key), head)), params), url);
+// findParam :: String -> IO Maybe [String]
+const findParam = key => map(compose(Maybe.of, find(compose(eq(key), head)), params), url);
 
 // -- Impure calling code ----------------------------------------------
 
 // run it by calling $value()!
 findParam('searchTerm').$value();
-// Just([['searchTerm', 'wafflehouse']])
+// Just(['searchTerm', 'wafflehouse'])
 ```
 
 Our library keeps its hands clean by wrapping `url` in an `IO` and passing the buck to the caller. You might have also noticed that we have stacked our containers; it's perfectly reasonable to have a `IO(Maybe([x]))`, which is three functors deep (`Array` is most definitely a mappable container type) and exceptionally expressive.