Fix #12434 - Empty continuation line warning while building docker image

[daminisatya]

This is a parsing error for docker versions <= "17.09.0-ce" where it checks for both empty line and a comment line after a command.

But there is a fix for lastest docker versions - docker-archive/docker-ce@e25514e

which only checks for empty lines.

Please let me know if there is a need for this change. Thank you.

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[daminisatya]

Check CLA

[daminisatya]

/assign @bradtopol
/assign @tengqm

[netlify]

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[tengqm]

/lgtm

[daminisatya]

/assign @cody-clark

[cody-clark]

Thanks!

/approve

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