Cast idx to uint32 to fix compilation on i386 (#1118)
Cast idx to uint32 to fix compilation on i386 (#1118)

`env GOOS=linux GOARCH=386` go build no longer complains about integer overflow.

See https://github.com/dgraph-io/badger/issues/953#issuecomment-552241033
dgraph-io/badger,dgraph-io/badger