Section subscription modified, a small design

## Section subscription modified, a small design

Changes:
- Size font resized to 26px
- The label changed to "Súmate a la comunidad de datos abiertos de México." 
- Deleted the css extra classes in the button "Suscríbeme"

![bienvenida codeando mexico - 2](https://cloud.githubusercontent.com/assets/660973/3663548/0ae06930-11d4-11e4-89e8-8073c111e9f8.png)

Signed-off-by: Miguel Angel Gordian <miguel.angel@codeandomexico.org>