chore: Avoid using deprecated Buffer constructor (serialport#1510)

safe-buffer is already used and provides Buffer.alloc polyfill, so
just use Buffer.alloc directly to avoid hitting deprecated API.

Refs:
https://nodejs.org/api/deprecations.html#deprecations_dep0005_buffer_constructor

lib/bindings/mock.js

@@ -17,7 +17,7 @@ class MockBinding extends BaseBinding {
     this.isOpen = false;
     this.port = null;
     this.lastWrite = null;
-    this.recording = new Buffer(0);
+    this.recording = Buffer.alloc(0);
     this.writeOperation = null; // in flight promise or null
   }