[1.5.x] Fixed typo in docs/topics/conditional-view-processing.txt

The ``condition`` decorator is useful for more than only ``GET`` and

``HEAD`` requests (``HEAD`` requests are the same as ``GET`` in this

situation). It can be used also to be used to provide checking for ``POST``,

situation). It can also be used to provide checking for ``POST``,

``PUT`` and ``DELETE`` requests. In these situations, the idea isn't to return

a "not modified" response, but to tell the client that the resource they are

trying to change has been altered in the meantime.