fix jsonParamsToArgsWS index error
fix jsonParamsToArgsWS index error

Error from tendermint:
```
panic: runtime error: index out of range

goroutine 82 [running]:
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server.jsonParamsToArgsWS(0xc4200960e0, 0xc42024d4a0, 0xc420215380, 0x3, 0x0, 0x0, 0xc420215383, 0x9, 0xc42024d4a0, 0xf1ecc0, ...)
        /home/vagrant/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server/handlers.go:184 +0x654
github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server.(*wsConnection).readRoutine(0xc4201fd0e0)
        /home/vagrant/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server/handlers.go:496 +0x3a9
created by github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server.(*wsConnection).OnStart
        /home/vagrant/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/go-rpc/server/handlers.go:377 +0x45
```

tendermint/tendermint,tendermint/go-rpc,tendermint/go-rpc,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint