adjusted Dockerfile

src/test/resources/docker/mxnet/Dockerfile

@@ -3,10 +3,11 @@ FROM maven:3-jdk-8
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         git \
+        libgtk2.0-dev \
         wget python gcc \
         build-essential cmake \
         liblapack-dev libblas-dev libboost-dev libarmadillo-dev && \
-    rm -rf /var/lib/apt/lists/* 
+    rm -rf /var/lib/apt/lists/*
 RUN git clone https://github.com/apache/incubator-mxnet.git mxnet-source && \
     cd mxnet-source && git checkout tags/1.4.0 && cd .. && \
     cp -r mxnet-source/include/mxnet /usr/include/mxnet && \