Fix uplift_drf_demo failure

[wendycwong]

I tried to run it locally and run into error here:

I have uploaded the data to h2o-public-test-data/bigdata/server on S3.

The path to the dataset is now:

"https://s3.amazonaws.com/h2o-public-test-data/bigdata/server/criteo-uplift-v2.1.csv"

This dataset is from Kaggle and it can time out when trying to load the file and as a result the test will fail.

I tried to change the path to pd.read_csv and it does not work. Probably set something wrong somewhere.