[ubuntu 18.04] Update MXNet to 1.3.1

ubuntu-18.04/Dockerfile

@@ -71,11 +71,11 @@ RUN python3.6 -m pip --no-cache-dir install \
         psutil
 
 RUN cd /opt && \
-    curl -sSLO https://github.com/apache/incubator-mxnet/releases/download/1.3.0/apache-mxnet-src-1.3.0-incubating.tar.gz && \
-    tar -xf apache-mxnet-src-1.3.0-incubating.tar.gz --owner root --group root --no-same-owner && \
-    rm -f apache-mxnet-src-1.3.0-incubating.tar.gz && \
-    mv apache-mxnet-src-1.3.0-incubating mxnet-1.3.0 && \
-    cd mxnet-1.3.0 && \
+    curl -sSLO https://github.com/apache/incubator-mxnet/releases/download/1.3.1/apache-mxnet-src-1.3.1.rc0-incubating.tar.gz && \
+    tar -xf apache-mxnet-src-1.3.1.rc0-incubating.tar.gz --owner root --group root --no-same-owner && \
+    rm -f apache-mxnet-src-1.3.1.rc0-incubating.tar.gz && \
+    mv apache-mxnet-src-1.3.1.rc0-incubating mxnet-1.3.1 && \
+    cd mxnet-1.3.1 && \
     cmake -Bbuild -H. \
         -DCMAKE_CXX_STANDARD=14 -DUSE_CXX14_IF_AVAILABLE=ON \
         -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr/local \