Replace Dockerfile with Containerfile

Dockerfile → Containerfile

@@ -1,6 +1,6 @@
 # Default to Go 1.13
 ARG GO_VERSION=1.13
-FROM golang:${GO_VERSION}-alpine as build
+FROM docker.io/library/golang:${GO_VERSION}-alpine as build
 
 # Necessary to run 'go get' and to compile the linked binary
 RUN apk add git musl-dev