message: fix example bug
diff: # See the License for the specific language governing permissions and
  # limitations under the License.
  # pylint: disable=doc-string-missing
  -from paddle_serving_server_gpu.web_service import WebService
  +from paddle_serving_server.web_service import WebService
  from paddle_serving_app.reader import ChineseBertReader
  import sys
  import os
  