Update Dockerfile

Dockerfile

@@ -1,6 +1,4 @@
-FROM alpine:3.6
+FROM alpine:edge
 MAINTAINER Jermine <Jermine.hu@qq.com>
-RUN apk add git=2.14.1-r1 \
-    --repository http://dl-cdn.alpinelinux.org/alpine/edge/main \
-    --no-cache
+RUN apk add git=2.14.2-r0 --no-cache
 CMD ["git"]