automatic deployment to s3

To keep the behaviour consistent with grunt-s3, I would like to use defaults instead:
```javascript
              credentials : {
                  accessKeyId: this.data.key ? this.data.key : process.env.AWS_ACCESS_KEY_ID,
                  secretAccessKey: this.data.secret ? this.data.secret : process.env.AWS_SECRET_ACCESS_KEY,
                  region: this.data.region ? this.data.region : 'us-east-1'
```