Be more explicit to avoid decode error in python3 (onnx#97)

Author: guang

tutorials/PytorchCaffe2MobileSqueezeNet.ipynb

@@ -287,9 +287,9 @@
  ],
  "source": [
  "# Verify it runs with predictor\n",
- "with open(\"squeeze_init_net.pb\") as f:\n",
+ "with open(\"squeeze_init_net.pb\", \"rb\") as f:\n",
  " init_net = f.read()\n",
- "with open(\"squeeze_predict_net.pb\") as f:\n",
+ "with open(\"squeeze_predict_net.pb\", \"rb\") as f:\n",
  " predict_net = f.read()\n",
  "from caffe2.python import workspace\n",
  "p = workspace.Predictor(init_net, predict_net)\n",