Update sample-lnd.conf

bitcoin.rpcpolling has to be set to true, otherwise malformed key=value (bitcoind.rpcpolling) error happens during initialization.

sample-lnd.conf

@@ -613,7 +613,7 @@ bitcoin.node=btcd
 ; instead of using the zmq interface. Only the rpcpolling option needs to
 ; be set in order to enable this, the rest of the options can be used to
 ; change the default values used for this configuration.
-; bitcoind.rpcpolling
+; bitcoind.rpcpolling=true
 ; bitcoind.blockpollinginterval=1m
 ; bitcoind.txpollinginterval=30s