[UPGRADE] Homepage dockerfile

[chibenwa]

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

• dockerfiles/site/homepage/Dockerfile

We recommend upgrading to ruby:2.6.8-slim-buster, as this image has only 61 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
	714	Credentials Management SNYK-DEBIAN10-PYTHON37-349025	No Known Exploit
	714	Directory Traversal SNYK-DEBIAN10-PYTHON37-452235	No Known Exploit
	714	Improper Input Validation SNYK-DEBIAN10-PYTHON37-461183	No Known Exploit
	714	Improper Input Validation SNYK-DEBIAN10-PYTHON37-584371	No Known Exploit
	714	NULL Pointer Dereference SNYK-DEBIAN10-SUBVERSION-1071814	No Known Exploit

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