feat: add getTxChainLocks to RPC list and array to types

[coolaj86]

It's important to note that this takes an anonymous array as the parameter, not an object with a named key like other RPC calls in the library.

- rpc.getTxChainLocks({ txids: [ "xxxx..." ] });
+ rpc.getTxChainLocks([ "xxxx..." ]);

Re: #63

These May NOT be the Droids You're Looking For

InstantSend Lock (a.k.a. ISLock, LLMQ Lock) is NOT ChainLock.

Instead see the isInstantSendLock field from getRawTransaction.

Monkey Patch

This can be monkey-patched, for those waiting for this PR to get pulled in:

var RpcClient require('@dashevo/dashd-rpc');

RpcClient.callspec.getTxChainLocks = 'obj';

Note: this uses obj rather than array because the types can't be monkey-patched and the difference between the two is only semantic here.