chore(grunt): update to latest grunt to fix grunt bug when running on node 0.10.0

Changes to the path API in nodeJS causes the build to fail with grunt 0.4.0.  This patch fixes it in two ways:

- Update to grunt 0.4.1 - this version fixes the bug
- Add cwd option to build - this also fixes the issue but from our side and works with grunt 0.4.0
docs(README): add installation instructions