[Snyk] Security upgrade golang from 1.18.5 to 1.18.9

[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 golang:1.18.9, as this image has only 108 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
	611	Integer Overflow or Wraparound SNYK-DEBIAN11-LIBKSBA-3179188	No Known Exploit
	714	Out-of-bounds Read SNYK-DEBIAN11-LIBTASN16-3061097	No Known Exploit
	500	Out-of-bounds Read SNYK-DEBIAN11-PCRE2-2808697	No Known Exploit
	500	Out-of-bounds Read SNYK-DEBIAN11-PCRE2-2808704	No Known Exploit
	500	Out-of-bounds Write SNYK-DEBIAN11-ZLIB-2976151	No Known Exploit

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[fotos]

We need to update the README too (see #54) – or we need to remove the README references.