Dockerfile: Fix build, update base

Author: mrueg

Dockerfile

@@ -1,9 +1,9 @@
-FROM golang:1.17.8-alpine3.15 AS builder
+FROM golang:1.18.3-alpine3.16 AS builder
 WORKDIR /go/src/github.com/mrueg/netcupscp-exporter
 COPY . .
 RUN apk --no-cache add make git && make
 
-FROM scratch
+FROM alpine:3.16
 COPY --from=builder /go/src/github.com/mrueg/netcupscp-exporter/netcupscp-exporter /
 
 CMD ["/netcupscp-exporter"]