Fix title of reduce method exercise (#653)

Author: chvmvd

docs/2-browser-apps/04-anonymous-function/index.mdx

@@ -179,7 +179,7 @@ const minScore = scores.reduce(/* コールバック関数 */);
 document.write(minScore); // 55
 ```
 
-<Answer title="Array#reduceの使い方">
+<Answer title="Array#reduce メソッドの使い方">
 
 ```javascript
 const scores = [90, 65, 70, 55, 80];