RNN ONNX export: concat hidden/cell states on the right axis (#2055)
RNN ONNX export: concat hidden/cell states on the right axis (#2055)

Test Plan: existing tests in onnx-fb-universe catch this, modulo a bug
in the tests which I am fixing in a separate diff
Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,Yangqing/caffe2,caffe2/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2