Correct 'Redis Cache' reference document title.

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
Original pull request #2459

src/main/asciidoc/reference/redis-cache.adoc

@@ -1,5 +1,5 @@
 [[redis:support:cache-abstraction]]
-== Redis Cache
+= Redis Cache
 
 NOTE: Changed in 2.0