docker: bump to golang:1.16.5-alpine3.13

docker: bump to golang:1.16.5-alpine3.13

diff --git a/Dockerfile b/Dockerfile
index 38cb524..d244fc0 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.15.5-alpine3.12 AS builder
+FROM golang:1.16.5-alpine3.13 AS builder
 
 RUN apk -v --no-progress --no-cache add git
 

GitHub sha: 0dbd380f