rpc: update lnd to be compatible with btcd master

[Roasbeef]

The latest version of btcd master broke an existing API, by taking a value that was a bool and making it an int (or the other way around). Similar to what we've done in the past w.r.t probing to see which versions are supported, we also need to patch in this change. Ideally we can prevent things like this on the btcd end, by just adding the new field if possible under a distinct name. The call in question is GetBlockVerboseTx: btcsuite/btcd#1529

[Roasbeef]

With the dependent PRs in now, we just need to update our go.mod, and then also travis to start building against that new commit.