Update rfe.py

Emphasizing that RFE needs at least 3 chunks to work.
Update rfe.py

Corrected RFE and SplitClassifier with 3 chunks for cross validation.
Update rfe.py

Typo!
Update rfe.py

Unnecessary space removed
Update rfe.py

reducing line length
Merge pull request #171 from armaneshaghi/master

Update rfe.py - add note that RFE needs >=3 chunks for cross-validation.