Update Dockerfile set default timezone to UTC.

docker/alpine/Dockerfile

@@ -11,7 +11,7 @@ ENV PASSWORD=
 ENV METHOD      aes-256-gcm
 ENV TIMEOUT     300
 ENV DNS_ADDRS    8.8.8.8,8.8.4.4
-ENV TZ Asia/Shanghai
+ENV TZ UTC
 ENV ARGS=
 
 COPY . /tmp/repo

docker/alpine/README.md

@@ -63,7 +63,7 @@ Besides `PASSWORD`, the image also defines the following environment variables t
 * `METHOD`: encryption method to use, defaults to `aes-256-gcm`
 * `TIMEOUT`: defaults to `300`
 * `DNS_ADDRS`: DNS servers to redirect NS lookup requests to, defaults to `8.8.8.8,8.8.4.4`
-* `TZ`: Timezone, defaults to `Asia/Shanghai`
+* `TZ`: Timezone, defaults to `UTC`
 
 Additional arguments supported by `ss-server` can be passed with the environment variable `ARGS`, for instance to start in verbose mode:
 ```bash