[Snyk] Security upgrade ubuntu from 18.04 to rolling

[snyk-bot]

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image.

Changes included in this PR

• Dockerfile

We recommend upgrading to ubuntu:rolling, as this image has only 13 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
	300	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	300	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	300	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	300	Improper Verification of Cryptographic Signature SNYK-UBUNTU1804-PERL-1930908	No Known Exploit
	150	Time-of-check Time-of-use (TOCTOU) SNYK-UBUNTU1804-SHADOW-306209	No Known Exploit

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