Thinned down Docker container. With this new setup container of this …

…app takes up only 17MP instead of previous 428MB.

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:alpine
+FROM golang:alpine as builder
 
 COPY . $GOPATH/src/github.com/rylio/ytdl/
 RUN apk update && apk upgrade && \
@@ -7,6 +7,7 @@ RUN go get -d github.com/rylio/ytdl/cmd/ytdl/
 RUN apk del git
 WORKDIR $GOPATH/src/github.com/rylio/ytdl/cmd/ytdl/
 RUN go build -o /go/bin/ytdl
-WORKDIR /ytdl/
 
-ENTRYPOINT ["/go/bin/ytdl"]
+FROM alpine
+COPY --from=builder /go/bin/ytdl /go/bin/ytdl
+ENTRYPOINT ["/go/bin/ytdl"]