Fixed silly whitespace error in cache docs.

The per-site cache

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**New in Django development version** (previous versions of Django only provided a single ``CacheMiddleware`` instead of the two pieces described below).

**New in Django development version** (previous versions of Django only provided

a single ``CacheMiddleware`` instead of the two pieces described below).

Once the cache is set up, the simplest way to use caching is to cache your

entire site. You'll need to add