[Snyk] Security upgrade ubuntu from 18.04 to impish-20211015

[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

• docker/puppet-bolt/Dockerfile

We recommend upgrading to ubuntu:impish-20211015, as this image has only 14 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
	371	Buffer Overflow SNYK-UBUNTU1804-GLIBC-2356802	No Known Exploit
	371	Buffer Overflow SNYK-UBUNTU1804-GLIBC-2356854	No Known Exploit
	371	Buffer Overflow SNYK-UBUNTU1804-GLIBC-2356854	No Known Exploit
	371	CVE-2021-3999 SNYK-UBUNTU1804-GLIBC-2359261	No Known Exploit
	371	CVE-2021-3999 SNYK-UBUNTU1804-GLIBC-2359261	No Known Exploit

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[rileynewton]

@donoghuc Ha, I just hit the button to do this since I was curious, but this Docker container is broken currently anyway, should we just go through with the upgrade?

[donoghuc]

It would probably be good to build it manually just to make sure but this looks like a fine change to me.