fix 2.7 closures

source/chapter2/07_Closures.md

@@ -103,7 +103,7 @@ var reversed = sort(names, backwards)
 ```
 reversed = sort(names, { (s1: String, s2: String) -> Bool in
     return s1 > s2
-    })
+})
 ```
 
 需要注意的是内联闭包参数和返回值类型声明与`backwards`函数类型声明相同。