fix: unsubscribe fails depending on channel id type

`Object.keys` casts to strings, channel ids can be are
numbers, the compare function does not cast.

in general its faster to do a direct object access instead of
converting to an array and doing a search on the array.

Author: robertkowalski

lib/transports/ws2.js

@@ -233,7 +233,7 @@ class WSv2 extends EventEmitter {
    * @returns {boolean} isSubscribed
    */
   hasChannel (chanId) {
-    return _includes(Object.keys(this._channelMap), chanId)
+    return !!this._channelMap[chanId]
   }
 
   /**

test/lib/transports/channels.js

@@ -0,0 +1,43 @@
+/* eslint-env mocha */
+
+'use strict'
+
+const assert = require('assert')
+
+const WSv2 = require('../../../lib/transports/ws2')
+
+const API_KEY = 'dummy'
+const API_SECRET = 'dummy'
+
+const createTestWSv2Instance = (params = {}) => {
+  return new WSv2({
+    apiKey: API_KEY,
+    apiSecret: API_SECRET,
+    url: 'ws://localhost:9997',
+    ...params
+  })
+}
+
+describe('WSv2 channels', () => {
+  it('numeric and string channel ids work', () => {
+    const ws = createTestWSv2Instance()
+
+    ws._channelMap = {
+      83297: {
+        event: 'subscribed',
+        channel: 'book',
+        chanId: 83297,
+        symbol: 'tADAUSD',
+        prec: 'P0',
+        freq: 'F0',
+        len: '25',
+        pair: 'ADAUSD'
+      }
+    }
+
+    assert.strictEqual(ws.hasChannel(83297), true)
+    assert.strictEqual(ws.hasChannel('83297'), true)
+    assert.strictEqual(ws.hasChannel('1337'), false)
+    assert.strictEqual(ws.hasChannel(1337), false)
+  })
+})