Have to create .grunt\grunt-gh-pages\gh-pages\src manually

On my machine (Windows 8 64bit, nodejs v0.10.17, git version 1.8.3.msysgit.0), running `grunt gh-pages` failed with:

```
Running "gh-pages:src" (gh-pages) task
Cloning https://github.com/andyli/ResearchSeminar.git into .grunt\grunt-gh-pages\gh-pages\src
Warning: fatal: could not create work tree dir '.grunt\grunt-gh-pages\gh-pages\src'.: No such file or directory
 Use --force to continue.
```

If I manually create the *.grunt\grunt-gh-pages\gh-pages\src* folder before running the task, it will success.