message: Copy example contracts before cleaning up source
  Example contracts are now located in `/opt/eos/contracts`.
  Testers can run the compiles contracts(`.wast`), for example,
  ```
  sudo docker exec eos /opt/eos/bin/eosc setcode currency opt/eos/contracts/currency/currency.wast opt/eos/contracts/currency/currency.abi
  ```
diff: @@ -48,13 +48,15 @@ RUN cd /tmp && wget https://gmplib.org/download/gmp/gmp-6.1.2.tar.bz2 \
  && make check \
  && rm -rf /tmp/gmp-6.1.2
  +RUN mkdir -p /opt/eos/bin/data-dir
  +
  RUN cd /tmp && git clone https://github.com/EOSIO/eos.git --recursive \
  && cd eos && mkdir build && cd build \
  && WASM_LLVM_CONFIG=/opt/wasm/bin/llvm-config cmake -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_INSTALL_PREFIX=/opt/eos ../ \
  && make -j2 && make install \
  + && cp -a ../contracts /opt/eos/contracts \
  && rm -rf /tmp/eos*
  -RUN mkdir -p /opt/eos/bin/data-dir
  COPY config.ini genesis.json /
  COPY entrypoint.sh /sbin
  RUN cd /opt/eos/bin && chmod +x /sbin/entrypoint.sh
  