Add multi-model capability label to 1.4.0 Dockerfile (#54)

Author: ajaykarpur

docker/1.4.0/py3/Dockerfile.cpu

@@ -2,6 +2,7 @@ FROM ubuntu:16.04
 
 LABEL maintainer="Amazon AI"
 LABEL com.amazonaws.sagemaker.capabilities.accept-bind-to-port=true
+LABEL com.amazonaws.sagemaker.capabilities.multi-models=true
 
 ARG PYTHON_VERSION=3.6.6
 ARG PYTORCH_VERSION=1.4.0