use alpine for docker

Dockerfile

@@ -1,15 +1,32 @@
 FROM golang:1.12-alpine AS builder
 WORKDIR /src
 COPY . .
-RUN \
-    apk add taglib-dev sqlite build-base git && \
+RUN apk add -U --no-cache \
+        build-base \
+        ca-certificates \
+        git \
+        sqlite \
+        taglib-dev && \
     ./_do_build_server && \
     ./_do_build_scanner && \
-    apk del build-base && \
-    mv ./gonic ./gonicscan /bin/
+    apk del build-base
+
+FROM alpine
+COPY --from=builder \
+    /etc/ssl/certs/ca-certificates.crt \
+    /etc/ssl/certs/
+COPY --from=builder \
+    /usr/lib/libgcc_s.so.1 \
+    /usr/lib/libstdc++.so.6 \
+    /usr/lib/libtag.so.1 \
+    /usr/lib/
+COPY --from=builder \
+    /src/gonic \
+    /src/gonicscan \
+    /bin/
 VOLUME ["/data", "/music"]
 EXPOSE 80
-ENV GONIC_LISTEN_ADDR :80
 ENV GONIC_DB_PATH /data/gonic.db
+ENV GONIC_LISTEN_ADDR :80
 ENV GONIC_MUSIC_PATH /music
 CMD ["gonic"]