update v0.6.2 panic

[xjtdy888]

goroutine 52 [running]:
runtime/internal/atomic.goXadd64(0x257e10c, 0x1, 0x0, 0x22f36d0, 0x149ec)
        /usr/local/go/src/runtime/internal/atomic/atomic_arm.go:103 +0x1c
github.com/centrifugal/centrifuge-go.(*Subscription).nextFutureID(...)
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/subscription.go:174
github.com/centrifugal/centrifuge-go.(*Subscription).onSubscribe(0x257e0c0, 0x22f36e0)
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/subscription.go:244 +0xbc
github.com/centrifugal/centrifuge-go.(*Subscription).history(0x257e0c0, 0x22f36d0)
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/subscription.go:275 +0x54
github.com/centrifugal/centrifuge-go.(*Subscription).History(0x257e0c0, 0x18bf630, 0x44, 0x5040000, 0x3, 0x3)
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/subscription.go:207 +0x90
xxxxxxxxxxxx.com/xxxxxxxxxxxx/lib/tracker.(*subEventHandler).OnSubscribeSuccess(0x1c46200, 0x257e0c0, 0x0)
        /work/go/src/xxxxxxxxxxxx.com/xxxxxxxxxxxx/lib/tracker/event.go:70 +0x150
github.com/centrifugal/centrifuge-go.(*Subscription).subscribeSuccess.func1()
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/subscription.go:357 +0x3c
github.com/centrifugal/centrifuge-go.(*cbQueue).dispatch(0x23686e0)
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/queue.go:44 +0x90
created by github.com/centrifugal/centrifuge-go.New
        /work/go/pkg/mod/github.com/centrifugal/centrifuge-go@v0.6.2/client.go:124 +0x4c4