message: Update build.Dockerfile
  Fix the syntax error
diff: @@ -33,7 +33,7 @@ RUN git clone https://github.com/NVIDIA/HugeCTR.git &&\
  git submodule update --init --recursive && \
  mkdir build && cd build &&\
  cmake -DCMAKE_BUILD_TYPE=$CMAKE_BUILD_TYPE -DSM=$SM \
  - -DVAL_MODE=$VAL_MODE -DENABLE_MULTINODES=$ENABLE_MULTINODES -DNCCL_A2A=NCCL_A2A .. && \
  + -DVAL_MODE=$VAL_MODE -DENABLE_MULTINODES=$ENABLE_MULTINODES -DNCCL_A2A=$NCCL_A2A .. && \
  make -j &&\
  mkdir /usr/local/hugectr &&\
  make install &&\
  