[Snyk] Security upgrade ubuntu from bionic to 18.04

[reachfh]

This PR was automatically created by Snyk using the credentials of a real user.

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

• docker/Dockerfile.build.script

We recommend upgrading to ubuntu:18.04, as this image has only 16 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	Issue	Exploit Maturity
	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	Information Exposure SNYK-UBUNTU1804-GCC8-572149	No Known Exploit
	Off-by-one Error SNYK-UBUNTU1804-SYSTEMD-3098847	No Known Exploit
	Out-of-bounds Read SNYK-UBUNTU1804-TAR-3261139	No Known Exploit

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