[fluentd-elasticsearch] typo in ENABLE_ILM environment variable

[niklaskhf]

Fix typo'd single quote

A typo in the ENABLE_ILM environment variable didn't get caught previously .

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] DCO signed
• [x] Chart Version bumped (if the pr is an update to an existing chart)
• [x] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [fluentd-elasticsearch])

[niklaskhf]

Apologies for missing the typo previously.