Update Dockerfile

Dockerfile

@@ -1,6 +1,6 @@
 FROM alpine:3.6
 MAINTAINER Jermine <Jermine.hu@qq.com>
-RUN apk add git=2.14.1-r1 \
+RUN apk add git \
     --repository http://dl-cdn.alpinelinux.org/alpine/edge/main \
     --no-cache
 ENTRYPOINT ["/bin/sh"]