Fix bower's relative path to absolute path in H5BP template

Fix a following problem.

# Expected

```bash
$ yo jekyllrb
# * Select H5BP template
# * And select 'Add H5★BP javascript files?' to YES
# * And select 'Choose a post permalink style' to pretty

$ grunt server

# Open Chrome web browser
$ open http://localhost:9000/jekyll/update/2013/09/02/yo-jekyllrb/
# Open JavaScript Console
(CTRL-SHIFT-J in Chrome)
```

There are **no errors in JavaScript Console**. 

# Actual

Same as above, and...

There is **an error in JavaScript Console**. 

![generator-jekyllrb_fix-bower](https://f.cloud.github.com/assets/20859/1064184/ce8c9488-1317-11e3-8262-4bef43510e9c.png)