refactor(cb): all callback renamed to cb, and local callbacks to _cb

lib/postgresql_interface.js

@@ -117,18 +117,18 @@ exports.getTxs = function getTxs(txId, cb) {
 exports.getPendingAmount = function getPendingAmount(txId, cb) {
   async.parallel({
     // NOTE: `async.apply()` would strip context here
-    txs: function(callback) {
+    txs: function(_cb) {
       client.query(
         'SELECT * FROM transactions WHERE id=$1',
         [txId],
-        callback
+        _cb
       );
     },
-    bills: function(callback) {
+    bills: function(_cb) {
       client.query(
         'SELECT * FROM bills WHERE transaction_id=$1 ORDER BY created DESC',
         [txId],
-        callback
+        _cb
       );
     }
   }, function(err, results) {