[MINOR] Added scikit learn as dependency for systemml pip package
[MINOR] Added scikit learn as dependency for systemml pip package

- Without this fix, running a simple mlcontext example after `pip
install systemml` will result in an error.
asurve/systemml,deroneriksson/incubator-systemml,nakul02/incubator-systemml,asurve/systemml,dusenberrymw/incubator-systemml,dusenberrymw/systemml,nakul02/systemml,apache/incubator-systemml,gweidner/incubator-systemml,nakul02/systemml,niketanpansare/systemml,dhutchis/systemml,niketanpansare/systemml,deroneriksson/incubator-systemml,asurve/incubator-systemml,gweidner/systemml,niketanpansare/incubator-systemml,apache/incubator-systemml,nakul02/systemml,asurve/arvind-sysml2,asurve/systemml,dusenberrymw/systemml,nakul02/incubator-systemml,dhutchis/systemml,niketanpansare/incubator-systemml,asurve/arvind-sysml2,niketanpansare/incubator-systemml,asurve/incubator-systemml,asurve/arvind-sysml2,asurve/systemml,deroneriksson/systemml,gweidner/incubator-systemml,gweidner/systemml,dusenberrymw/systemml,nakul02/systemml,niketanpansare/incubator-systemml,deroneriksson/systemml,niketanpansare/systemml,dusenberrymw/incubator-systemml,nakul02/systemml,dhutchis/systemml,gweidner/systemml,deroneriksson/incubator-systemml,deroneriksson/systemml,deroneriksson/incubator-systemml,apache/incubator-systemml,asurve/incubator-systemml,dhutchis/systemml,asurve/arvind-sysml2,deroneriksson/systemml,nakul02/systemml,dhutchis/systemml,apache/incubator-systemml,apache/incubator-systemml,dusenberrymw/incubator-systemml,asurve/incubator-systemml,asurve/incubator-systemml,gweidner/systemml,deroneriksson/systemml,apache/incubator-systemml,dusenberrymw/systemml,gweidner/systemml,deroneriksson/incubator-systemml,asurve/arvind-sysml2,gweidner/incubator-systemml,asurve/systemml,gweidner/incubator-systemml,dusenberrymw/systemml,deroneriksson/systemml,niketanpansare/systemml,dusenberrymw/systemml,deroneriksson/incubator-systemml,gweidner/incubator-systemml,nakul02/incubator-systemml,nakul02/incubator-systemml,asurve/arvind-sysml2,nakul02/incubator-systemml,asurve/systemml,gweidner/systemml,niketanpansare/systemml,dusenberrymw/incubator-systemml,dhutchis/systemml,niketanpansare/systemml,gweidner/incubator-systemml,dusenberrymw/incubator-systemml,nakul02/incubator-systemml,asurve/incubator-systemml,dusenberrymw/incubator-systemml