change back end base image to alpine

Dockerfile

@@ -1,20 +1,23 @@
-FROM golang:1.13 as build
+FROM golang:1.13-alpine as build
 ARG RELEASE=TRUE
 WORKDIR /var/myrunes
 ADD . .
+
+RUN apk add git
 RUN go mod download
 RUN go build \
         -v -o /app/myrunes -ldflags "\
             -X github.com/myrunes/backend/internal/static.Release=${RELEASE} \
             -X github.com/myrunes/backend/internal/static.AppVersion=$(git describe --tags --abbrev=0)+$(git describe --tags | sed -n 's/^[0-9]\+\.[0-9]\+\.[0-9]\+-\([0-9]\+\)-.*$/\1/p')" \
         ./cmd/server/*.go
 
-FROM debian:stretch-slim AS final
+# ----------------------------------------------------------
+
+FROM alpine:latest AS final
 LABEL maintainer="zekro <contact@zekro.de>"
-RUN apt-get update &&\
-    apt-get install -y ca-certificates &&\
-    update-ca-certificates
 WORKDIR /app
+
+RUN apk add ca-certificates
 COPY --from=build /app .
 
 EXPOSE 8080