Minor table cells styling on READMEs

Before:
![before](https://f.cloud.github.com/assets/620714/931687/ace41d54-0031-11e3-82cb-cdbc01c86cdd.png)
After:
![after](https://f.cloud.github.com/assets/620714/931686/acc937b4-0031-11e3-8fee-42027827c92e.png)