Fix issue allegro#21: "node-worker don't run in windows"

- in transport.send(), only call pipe.write once

Payload of second call (containing `serializedMessage`) was getting lost, or at least not being received.

I could not discern the exact root cause (something something pipes on windows).

Tests are all passing on linux and windows.

lib/worker/transport.js

@@ -52,11 +52,18 @@ class Transport extends EventEmitter {
 
     send(message) {
         const serializedMessage = msgpack.encode(message);
-        const header = new Uint32Array([ serializedMessage.byteLength ]);
+        const payloadLength = serializedMessage.byteLength;
 
-        this.pipe.write(Buffer.from(header.buffer));
-        this.pipe.write(serializedMessage);
+        const header = new Uint32Array([payloadLength]);
+        const headerLength = Uint32Array.BYTES_PER_ELEMENT * header.length;
+
+        this.pipe.write(
+            Buffer.concat(
+                [Buffer.from(header.buffer), serializedMessage],
+                payloadLength + headerLength
+            )
+        );
     }
 }
 
-module.exports = Transport;
+module.exports = Transport;