Use xenial for docker

docker/Dockerfile

@@ -1,10 +1,11 @@
-FROM ubuntu:trusty
+FROM ubuntu:xenial
 
 # http://fabiorehm.com/blog/2014/09/11/running-gui-apps-with-docker/
 RUN export uid=1000 gid=1000 && \
     mkdir -p /home/developer && \
     echo "developer:x:${uid}:${gid}:Developer,,,:/home/developer:/bin/bash" >> /etc/passwd && \
     echo "developer:x:${uid}:" >> /etc/group && \
+    mkdir -p /etc/sudoers.d && \
     echo "developer ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers.d/developer && \
     chmod 0440 /etc/sudoers.d/developer && \
     chown ${uid}:${gid} -R /home/developer
@@ -13,22 +14,16 @@ RUN \
   apt-get update -qq && \
   apt-get upgrade -qq -y && \
   apt-get install -qq -y \
-    aptitude \
     git \
-    python \
-    python-setuptools
+    python3 \
+    python3-pip
 
 RUN \
-  easy_install -q pip && \
-  pip install -q -U pip setuptools
-
-RUN apt-get install -qq -y python-qt4 pyqt4-dev-tools
-RUN apt-get install -qq -y python-matplotlib
-RUN apt-get install -qq -y python-scipy
-RUN apt-get install -qq -y python-skimage
-RUN apt-get install -qq -y python-tornado
+  apt-get install -qq -y \
+    python3-matplotlib \
+    python3-pyqt5
 
-RUN pip install -v git+https://github.com/wkentaro/labelme.git
+RUN pip3 install -v git+https://github.com/wkentaro/labelme.git
 
 USER developer
 ENV HOME /home/developer