add missed comma
add missed comma

Summary: D4205610 missed a comma , causing unnecessary logspill with WeightedSum op

Reviewed By: Yangqing

Differential Revision: D4222806

fbshipit-source-id: ff17c20eae7a7168475f39cc227d3e8ab347288f

bwasti/caffe2,bwasti/caffe2,sf-wind/caffe2,sf-wind/caffe2,davinwang/caffe2,davinwang/caffe2,Yangqing/caffe2,caffe2/caffe2,pietern/caffe2,davinwang/caffe2,bwasti/caffe2,sf-wind/caffe2,Yangqing/caffe2,pietern/caffe2,sf-wind/caffe2,sf-wind/caffe2,xzturn/caffe2,xzturn/caffe2,pietern/caffe2,xzturn/caffe2,bwasti/caffe2,pietern/caffe2,xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,xzturn/caffe2,pietern/caffe2,davinwang/caffe2,bwasti/caffe2