Correct 'Redis Cache' reference document title.

[jxblum]

Change redis-cache.adoc document title from '==' to '=' to appear as section 10.15 instead of 10.14.1, which currently places the 'Redis Cache' ref doc under 'Redis Scripting'.

Closes #2458

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[mp911de]

Thank you for your contribution. That's merged and backported now.