ec2-ami-tools: depends on ruby

[iMichka]

Fixes:
Error: ==> Testing ec2-ami-tools
==> /home/linuxbrew/.linuxbrew/Cellar/ec2-ami-tools/1.5.7_2/bin/ec2-ami-tools-version
/home/linuxbrew/.linuxbrew/Cellar/ec2-ami-tools/1.5.7_2/libexec/bin/ec2-ami-tools-version: line 6: ruby: command not found

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

---

[BrewTestBot]

🤖 A scheduled task has triggered a merge.