Update Dockerfile references to use 1.3

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.2
+# syntax=docker/dockerfile:1.3
 
 ARG DOCKERD_VERSION=19.03
 ARG CLI_VERSION=19.03

hack/dockerfiles/docs.Dockerfile

@@ -1,4 +1,4 @@
-# syntax = docker/dockerfile:1.2
+# syntax=docker/dockerfile:1.3
 
 FROM golang:1.16-alpine AS docsgen
 WORKDIR /src

hack/dockerfiles/lint.Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.2
+# syntax=docker/dockerfile:1.3
 
 FROM golang:1.16-alpine
 RUN apk add --no-cache gcc musl-dev yamllint

hack/dockerfiles/vendor.Dockerfile

@@ -1,4 +1,4 @@
-# syntax = docker/dockerfile:1.2
+# syntax=docker/dockerfile:1.3
 
 FROM golang:1.16-alpine AS vendored
 RUN  apk add --no-cache git rsync