Dockerfile: use syntax=docker/dockerfile:1

Now that HEREDOC is included in the stable Dockerfile syntax, we can
use the latest stable syntax for all Dockerfiles.

The recommendation for the stable syntax is to use `:1` (which is
equivalent to "latest" stable syntax.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3
+# syntax=docker/dockerfile:1
 
 ARG BASE_VARIANT=alpine
 ARG GO_VERSION=1.16.11

dockerfiles/Dockerfile.authors

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3-labs
+# syntax=docker/dockerfile:1
 
 FROM alpine:3.14 AS gen
 RUN apk add --no-cache bash git

dockerfiles/Dockerfile.dev

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3
+# syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.16.11
 

dockerfiles/Dockerfile.lint

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3
+# syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.16.11
 ARG GOLANGCI_LINT_VERSION=v1.23.8

dockerfiles/Dockerfile.shellcheck

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3
+# syntax=docker/dockerfile:1
 
 FROM koalaman/shellcheck-alpine:v0.7.1 AS shellcheck
 WORKDIR /go/src/github.com/docker/cli

dockerfiles/Dockerfile.vendor

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.3-labs
+# syntax=docker/dockerfile:1
 
 ARG GO_VERSION=1.16.11
 ARG MODOUTDATED_VERSION=v0.8.0