Query: Unit tests does not run properly with go 1.11

Unit tests uner test/filestore and test/multistore do not run properly with go 1.11. There are a lot of build error messages like this:

1. github.com/couchbase/query/test/gsi
   gsi/json.go:677: Println arg list ends with redundant newline

With older go versions this used to work fine.

Note that the fix only involves test files (unit tests), and does not affect server behavior at all.