message: Update builder to Ubuntu 18.04 LTS
diff: -FROM ubuntu:16.04
  +FROM ubuntu:18.04
  LABEL author="xiaobo <peterwillcn@gmail.com>" maintainer="Xiaobo <peterwillcn@gmail.com> Huang-Ming Huang <huangh@objectcomputing.com>" version="0.1.1" \
  description="This is a base image for building eosio/eos"
  @@ -6,7 +6,7 @@ LABEL author="xiaobo <peterwillcn@gmail.com>" maintainer="Xiaobo <peterwillcn@gm
  RUN echo 'APT::Install-Recommends 0;' >> /etc/apt/apt.conf.d/01norecommends \
  && echo 'APT::Install-Suggests 0;' >> /etc/apt/apt.conf.d/01norecommends \
  && apt-get update \
  - && DEBIAN_FRONTEND=noninteractive apt-get install -y sudo wget curl net-tools ca-certificates unzip
  + && DEBIAN_FRONTEND=noninteractive apt-get install -y sudo wget curl net-tools ca-certificates unzip gnupg
  RUN echo "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-4.0 main" >> /etc/apt/sources.list.d/llvm.list \
  && wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add - \
  