docs(readme): fix

Author: teppeis

README.md

@@ -35,7 +35,9 @@ You can set test directory in your `package.json`
 
 Then, run mocha with `--compilers js:espower-typescript/guess`
 
-    $ mocha --compilers js:espower-typescript/guess spec/**/*.js
+```console
+$ mocha --compilers ts:espower-typescript/guess spec/**/*.ts
+```
 
 Note: `'espower-typescript/guess'` is inspired by [intelli-espower-loader](https://github.com/azu/intelli-espower-loader)