Only install necessary packages

Author: SuperSandro2000

Dockerfile

@@ -1,13 +1,12 @@
 FROM golang:1.12-alpine AS build
 WORKDIR /go/src/github.com/factoriotools/factorio-docker-watchdog
-RUN apk add --no-cache alpine-sdk
+RUN apk add --no-cache g++ git
 COPY . .
 RUN go get ./... && \
   go build -a -installsuffix cgo -o app .
 
 FROM alpine
-RUN adduser -D -u 678 watchdog && \
-  apk add --no-cache alpine-sdk
+RUN adduser -D -u 678 watchdog
 USER watchdog
 COPY --from=build /go/src/github.com/factoriotools/factorio-docker-watchdog/app /app
 ENTRYPOINT ["/app"]