Fix highlight error

add highliht of `do:`
remove highlight of `function`

preview is 

![preview](https://f.cloud.github.com/assets/3627395/2316912/b12768e2-a33f-11e3-8c30-8e2ae98a795c.png)

now is 

![now](https://f.cloud.github.com/assets/3627395/2316917/c16f6da8-a33f-11e3-8cd4-1e937164cc80.png)