fix typo in cache documentation where it has catch.invalidate() instead of cache.invalidate()

[mikereiche]

[BKaneAtWork]

On this same line in the docs, please also change "primary key" to "primary index" and "bucket" to "collection". And remove the ":leveloffset: -1" text at the end of the line (or fix whatever that's supposed to be).

[mikereiche]

Note that to use cache.clear() or cache.invalidate(), the keyspace (bucket or collection) must have a primary index.