rename mempool.

lib/bcoin.js

@@ -113,7 +113,7 @@ bcoin.fullnode = require('./bcoin/fullnode');
 bcoin.chainblock = require('./bcoin/chainblock');
 bcoin.chaindb = require('./bcoin/chaindb');
 bcoin.chain = require('./bcoin/chain');
-bcoin.mempool = require('./bcoin/mempool2');
+bcoin.mempool = require('./bcoin/mempool');
 bcoin.keypair = require('./bcoin/keypair');
 bcoin.address = require('./bcoin/address');
 bcoin.walletdb = require('./bcoin/walletdb');