Dockerfile: Add checkstyle.jar at build time

Closes #50

Dockerfile

@@ -305,6 +305,10 @@ RUN curl -L 'http://downloads.sourceforge.net/project/fpgalibre/bakalint/0.4.0/b
   tar xf /tmp/bl.tar.gz -C /root/ && \
   find /tmp -mindepth 1 -prune -exec rm -rf '{}' '+'
 
+# Add checkstyle image
+RUN curl -fsSL https://github.com/coala/bear-runtime-deps/raw/master/CheckstyleBear/checkstyle-6.15-all.jar > /root/.local/share/coala-bears/CheckstyleBear/checkstyle-6.15-all.jar && \
+  find /tmp -mindepth 1 -prune -exec rm -rf '{}' '+'
+
 # Entrypoint script
 ADD docker-coala.sh /usr/local/bin/
 CMD ["/usr/local/bin/docker-coala.sh"]