docker: Multistage Docker build (#6)

Reducing image size approximately from 341MB to 16MB

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:alpine
+FROM golang:alpine AS builder
 
 EXPOSE 8000/tcp
 
@@ -17,3 +17,13 @@ RUN go get -v -d
 RUN go get github.com/GeertJohan/go.rice/rice
 RUN GOROOT=/go rice embed-go
 RUN go install -v
+
+
+FROM alpine
+
+EXPOSE 8000/tcp
+ENTRYPOINT ["pastebin"]
+
+COPY --from=builder /go/bin/pastebin /bin/pastebin
+
+