Fix docker image (#1101)

Fix #1099

substrate/Dockerfile

-FROM frolvlad/alpine-glibc AS builder
+FROM alpine:edge AS builder
 LABEL maintainer="chevdor@gmail.com"
 LABEL description="This is the build stage for Substrate. Here we create the binary."
 
 RUN apk add build-base \
     cmake \
     linux-headers \
-    openssl-dev && \
-    apk add --repository http://nl.alpinelinux.org/alpine/edge/community cargo
+    openssl-dev \
+    cargo
 
 ARG PROFILE=release
 WORKDIR /substrate