Fixing error message for layer model helper
Fixing error message for layer model helper

Summary: - Minor fix for error message in layer model helper file

Reviewed By: chocjy

Differential Revision: D5440768

fbshipit-source-id: df47bfe68a0caa750f0d3c8def28a5585e465ee0

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