Update Alpine to 3.12 from 3.7

Signed-off-by: inductor <kohei.ota@hpe.com>

nginx-golang-mysql/backend/Dockerfile

@@ -4,7 +4,7 @@ COPY . .
 
 RUN go build -o server .
 
-FROM alpine:3.7
+FROM alpine:3.12
 EXPOSE 8000
 COPY --from=build /go/src/github.com/org/repo/server /server
 CMD ["/server"]

nginx-golang-postgres/backend/Dockerfile

@@ -4,7 +4,7 @@ COPY . .
 
 RUN go build -o server .
 
-FROM alpine:3.7
+FROM alpine:3.12
 EXPOSE 8000
 COPY --from=build /go/src/github.com/org/repo/server /server
 CMD ["/server"]