[TwigBundle] minor #12309 fix markup twbs inline radio button

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12309 
| License       | MIT
| Doc PR        | N/A

This fixes a minor markup issue with the new bootstrap 3 form template.

**Before**
![before](https://cloud.githubusercontent.com/assets/930668/4767394/3c876d08-5b5d-11e4-9ab1-cbd93e2b5a70.png)

**After**
![after](https://cloud.githubusercontent.com/assets/930668/4767398/41213af6-5b5d-11e4-8156-302411ccf2ac.png)