npm install fails if libsass is not published

If you run an "npm publish" and libsass isn't included, then people doing an "npm install node-sass" get errrors.

See https://github.com/andrew/node-sass/issues/244

As a hotfix, you can include "git clone https://github.com/hcatlin/libsass" to the install command. This only works if end users have git installed (which might not be true for *all* node users).  The better solution is ensuring libsass is included whenever you run "npm publish".

```bash
# make 2 test directories
mkdir ~/node-sass-test1 && mkdir ~/node-sass-test2

# this test errors
cd ~/node-sass-test1
npm install git://github.com/andrew/node-sass.git

# this test works because libsass exists (after cloning)
cd ~/node-sass-test2
npm install git://github.com/skratchdot/node-sass.git
```