Fixed a bug that meant redis database numbers greater than zero (0) could not be used

For example
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If you give the Predis connector a connection dsn similar to `redis://127.0.0.1:6379/3`, the expected behaviour is to use redis database 3, it doesn't. 

It always uses redis db 0.

The fix was to correct a small typo in the Rhubarb/Connector/Predis file.