Update CONTRIBUTING.md

Removed inline triple backticks.

CONTRIBUTING.md

@@ -36,12 +36,12 @@ Your pull request should:
  
 The library sources are in: [src/lib](https://github.com/Microsoft/TypeScript/tree/master/src/lib)
 
-Library files in ```built/local/``` are updated by running
+Library files in `built/local/` are updated by running
 ```Shell
 jake
 ```
 
-The files in ```lib/``` are used to bootstrap compilation and usually do not need to be updated.
+The files in `lib/` are used to bootstrap compilation and usually do not need to be updated.
 
 #### `src/lib/dom.generated.d.ts` and `src/lib/webworker.generated.d.ts`