ref: use native promises instead of the 'async' lib

lib/index.js

@@ -1,8 +1,8 @@
 /* eslint-disable */
 
+const promisify = require('util').promisify;
 const http = require('http');
 const https = require('https');
-const async = require('async');
 
 function RpcClient(opts) {
   opts = opts || {};
@@ -25,9 +25,15 @@ function RpcClient(opts) {
     this.log = RpcClient.loggers[RpcClient.config.logger || 'normal'];
   }
 
-  this.queue = async.queue((task, callback) => {
-    task(callback);
-  }, queueSize);
+  this._chain = Promise.resolve();
+  this.queue = {
+    push: function (task) {
+      const taskAsync = promisify(task);
+      this._chain = this._chain.then(async function () {
+        await taskAsync();
+      });
+    },
+  };
 }
 
 const cl = console.log.bind(console);

package.json

@@ -43,7 +43,6 @@
     "coverage": "nyc npm run test"
   },
   "dependencies": {
-    "async": "^3.2.4",
     "bluebird": "^3.7.2"
   },
   "devDependencies": {