fix twitter account link, __underscore__ should be escaped

![open web platform daily digest 2013-09-18 22-11-58](https://f.cloud.github.com/assets/19714/1164995/e6e6ad1c-2063-11e3-9824-d6055aa095ad.jpg)

=>

![open web platform daily digest 2013-09-18 22-12-45](https://f.cloud.github.com/assets/19714/1164999/0297c8fc-2064-11e3-9840-6957edf3b413.jpg)