use latest version of alpine when building the Docker container

Signed-off-by: Adam Dobrawy <naczelnik@jawnosc.tk>

Dockerfile

@@ -16,7 +16,7 @@ WORKDIR $DISTRIBUTION_DIR
 COPY . $DISTRIBUTION_DIR
 RUN CGO_ENABLED=0 make PREFIX=/go clean binaries && file ./bin/registry | grep "statically linked"
 
-FROM alpine:3.9
+FROM alpine:3.10
 
 RUN set -ex \
     && apk add --no-cache ca-certificates apache2-utils