Update graceful-fs
Use rimraf and mkdirp instead of fs-extra
Update npm before installing

To support the new caret (^) syntax used by some dependencies, npm needs to be updated before installing on Node 0.8.  Updating the get-down module removes the dependency on the zlib package (using the built-in zlib module instead), which would not install/build with the latest npm.
Merge pull request #23 from tschaub/graceful

Force an update of `npm` before installing dependencies.  Packages whose dependencies are specified with caret syntax (e.g. `^3.2.1`) require parsing with [`semver@>=2.1.0`](isaacs/node-semver#41).  This means [`npm@>=1.3.7`](https://github.com/npm/npm/commit/f369647b00d5f9599046396c1721ca49bf1689ff) is needed.  Upgrading `npm` is required even if our versions are pegged.  It is common for our transitive dependencies to use fuzzy version matching which draws in newer packages that use the `^` syntax.

So, the first two changes here are unrelated to the build failure.  The build failure is fixed by forcing an upgrade of `npm` on Travis and updating `get-down` so it doesn't depend on a `zlib` package that is incompatible with the latest `npm`.