Database Close Method Typo

The Close method in this example is incorrectly documented. It should be Close() instead of close()

https://docs.couchbase.com/couchbase-lite/current/csharp/document.html#close-the-database 

I was getting the following error with close()

error CS1061: 'Database' does not contain a definition for 'close' and no accessible extension method 'close' accepting a first argument of type 'Database' could be found (are you missing a using directive or an assembly reference?) 

I created a PR to fix this as well on Github. 

https://github.com/couchbase/docs-couchbase-lite/pull/710