message: fix(npm): npm 5.6.0
diff: @@ -16,7 +16,7 @@ RUN mkdir /app
  WORKDIR /app
  # install npm 5.7.0 to fix https://github.com/npm/npm/issues/19356
  -RUN npm install -g npm@5.7.0
  +RUN npm install -g npm@5.6.0
  # install ionic
  RUN npm install -g ionic@3.20.0
  