fix opencv installation in dockerfile (#205)

docker/Dockerfile

@@ -7,7 +7,8 @@ RUN echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selectio
 
 # install basics
 RUN apt-get update -y \
- && apt-get install -y apt-utils git curl ca-certificates bzip2 cmake tree htop bmon iotop g++
+ && apt-get install -y apt-utils git curl ca-certificates bzip2 cmake tree htop bmon iotop g++ \
+ && apt-get install -y libglib2.0-0 libsm6 libxext6 libxrender-dev
 
 # Install Miniconda
 RUN curl -so /miniconda.sh https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh \
@@ -28,11 +29,10 @@ ENV PATH=$CONDA_PREFIX/bin:$PATH
 ENV CONDA_AUTO_UPDATE_CONDA=false
 
 RUN conda install -y ipython
-RUN pip install ninja yacs cython matplotlib
+RUN pip install ninja yacs cython matplotlib opencv-python
 
 # Install PyTorch 1.0 Nightly and OpenCV
 RUN conda install -y pytorch-nightly -c pytorch \
- && conda install -y opencv -c menpo \
  && conda clean -ya
 
 # Install TorchVision master