Fix Dockerfile to build on podman.

[junaruga]

Hello,

This commit fixes the following error on podman that is used mainly on Fedora, RHEL.

$ podman --version
podman version 3.4.4

$ podman build --build-arg BUILDER_NAME='Your Name' --build-arg BUILDER_EMAIL=your.name@example.com -t checkmake .
[1/2] STEP 1/5: FROM golang:1.13 AS builder
[1/2] STEP 2/5: ARG BUILDER_NAME BUILDER_EMAIL
[2/2] STEP 1/5: FROM alpine:3.9
Error: error building at STEP "ARG BUILDER_NAME BUILDER_EMAIL": ARG requires exactly one argument definition

Checklist

Not all of these might apply to your change but the more you are able to check
the easier it will be to get your contribution merged.

• CI passes
• Description of proposed change
• Documentation (README, docs/, man pages) is updated. => I think we don't need to update the documents for this PR.
• Existing issue is referenced if there is one
• Unit tests for the proposed change => Do you want to add docker/podman build case to CI?

[junaruga]

I am not sure why this PR's GitHub Actions is not executed.

[trinitronx]

I am not sure why this PR's GitHub Actions is not executed.

Maybe it's because permissions are needed? I just created a PR (#69) and it says this:

1 workflow awaiting approval
First-time contributors need a maintainer to approve running workflows.

[yegorich]

Fixes docker building for me too. My system: Ubuntu Bionic Beaver, Docker: 18.06.1-ce, build e68fc7a

[mrtazz]

thanks for taking the time to contribute!