Update docker builds to use Go 1.16 and Alpine Linux 3.13

Author: dhui

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.15-alpine3.12 AS builder
+FROM golang:1.16-alpine3.13 AS builder
 ARG VERSION
 
 RUN apk add --no-cache git gcc musl-dev make
@@ -15,7 +15,7 @@ COPY . ./
 
 RUN make build-docker
 
-FROM alpine:3.12
+FROM alpine:3.13
 
 RUN apk add --no-cache ca-certificates