fix some typos

Signed-off-by: cui fliter <imcusg@gmail.com>

assets/custom.js

@@ -110,7 +110,7 @@ var initAll = function () {
         pagePath = "index"
     }
 
-    // add vistors count
+    // add visitors count
     var ele = document.createElement("div");
     ele.setAttribute("align","center");
     var count = document.createElement("img")

assets/rustlings-zh/CHANGELOG.md

@@ -221,7 +221,7 @@
 #### Features
 
 *   add Option2 exercise (#290) ([86b5c08b](https://github.com/rust-lang/rustlings/commit/86b5c08b9bea1576127a7c5f599f5752072c087d))
-*   add excercise for option (#282) ([135e5d47](https://github.com/rust-lang/rustlings/commit/135e5d47a7c395aece6f6022117fb20c82f2d3d4))
+*   add exercise for option (#282) ([135e5d47](https://github.com/rust-lang/rustlings/commit/135e5d47a7c395aece6f6022117fb20c82f2d3d4))
 *   add new exercises for generics (#280) ([76be5e4e](https://github.com/rust-lang/rustlings/commit/76be5e4e991160f5fd9093f03ee2ba260e8f7229))
 * **ci:**  add buildkite config ([b049fa2c](https://github.com/rust-lang/rustlings/commit/b049fa2c84dba0f0c8906ac44e28fd45fba51a71))