* change css source to rawgit

Firefox complains that CSS file loaded from github.com is not the right MIME type and refuse to load it, whereas Chrome still can tolerate this error. 

```
The stylesheet https://raw.githubusercontent.com/oneyoung/jquery-calendar/master/css/style.css was not loaded because its MIME type, "text/plain", is not "text/css".
```
ref: <http://stackoverflow.com/questions/17341122/link-and-execute-external-javascript-file-hosted-on-github>