add plantuml package

Author: petrjasek

Dockerfile

@@ -30,6 +30,9 @@ RUN apt-get -y install \
     texlive-fonts-recommended latex-cjk-chinese-arphic-bkai00mp \
     latex-cjk-chinese-arphic-gbsn00lp latex-cjk-chinese-arphic-gkai00mp
 
+# Install plantuml
+RUN apt-get -y install plantuml
+
 # Install Python tools/libs
 RUN apt-get -y install python-pip && pip install -U virtualenv auxlib