Add installation of tzdata directly in the dockerfile.
FROM alpine:3.7
MAINTAINER Rethink
# Update Alpine's software source to a domestic (Tsinghua University) site, because pulling from the default official source is too slow...
# RUN echo "https://mirror.tuna.tsinghua.edu.cn/alpine/v3.4/main/" > /etc/apk/repositories
RUN apk update \
&& apk upgrade \
&& apk add --no-cache bash \
bash-doc \
bash-completion \
# timezone
tzdata \
&& rm -rf /var/cache/apk/* \
&& /bin/bash
RUN apk update \
&& apk upgrade \
&& apk add -U
RUN cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime