Deploy to cloudfoundry

This is for issue #193.
It requires `cf` cli tool installed inside the container. so a working configuration in `.drone.yml` is:

```
image: node:0.10
name: example-app
script:
  - npm config set ca ""
  - npm install
  # install cf tools
  - curl -O https://console.run.pivotal.io/downloads/cf-cli_amd64.deb
  - dpkg -i cf-cli_amd64.deb

deploy:
  cloudfoundry:
    target: https://api.run.pivotal.io
    username: <username>
    password: <pwd>
```