build: update Dockerfile to base image python:3-slim (#1)

Author: jiyungSong

Dockerfile

@@ -1,11 +1,13 @@
-FROM python:3.8
+FROM python:3-slim
 
 ENV PYTHONUNBUFFERED 1
 ENV SPACEONE_PORT 50051
 ENV SERVER_TYPE grpc
 ENV PKG_DIR /tmp/pkg
 ENV SRC_DIR /tmp/src
 
+RUN apt update && apt upgrade -y
+
 COPY pkg/*.txt ${PKG_DIR}/
 RUN pip install --upgrade pip && \
     pip install --upgrade -r ${PKG_DIR}/pip_requirements.txt && \