update some examples

Former-commit-id: 2ed7c323dd379eb68d5ccb2044cd9cc772ce0b08

_examples/tutorial/docker/Dockerfile

@@ -0,0 +1,17 @@
+# docker build -t myapp . 
+# docker run --rm -it -p 8080:8080 myapp:latest
+FROM golang:latest AS builder
+RUN apt-get update
+ENV GO111MODULE=on \
+    CGO_ENABLED=0 \
+    GOOS=linux \
+    GOARCH=amd64
+WORKDIR /go/src/app
+COPY go.mod .
+RUN go mod download
+COPY . .
+RUN go install
+
+FROM scratch
+COPY --from=builder /go/bin/app .
+ENTRYPOINT ["./app"]