Allow times (in RFC3339 format) in CSV test data

go-testdb is awesome and has saved me a lot of effort testing my database code.

It currently doesn't support time.Time objects (one of the standard types supported by driver.Value) in the CSV file.

My small enhancement below checks every string to see if it is in RFC3339 format. If it is, it is assumed to be a time.Time instead of a string.

If this is of use to you, please feel free to accept it upstream.