fix missing binary

Dockerfile

@@ -1,8 +1,8 @@
-FROM golang:1.16.2 AS builder
+FROM golang:1.16 AS builder
 WORKDIR /go/src/github.com/gliderlabs/registrator/
 COPY . .
-RUN go build -o bin/registrator .
+RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o /bin/registrator .
 
 FROM scratch
-COPY --from=builder /go/src/github.com/gliderlabs/registrator/bin/registrator /bin/registrator
+COPY --from=builder /bin/registrator /bin/registrator
 ENTRYPOINT ["/bin/registrator"]