Remove race condition between assemble and prelude load prints

emu.js

@@ -54,10 +54,11 @@ class Emulator {
 		this.print("Assembling kernel ");
 		const dots = setInterval(() => this.print("."), DOT_INTERVAL_MS);
 		this.worker = new Worker('boot.js', { type: 'module' });
-		this.worker.postMessage(this.mem);
+		this.worker.postMessage({ type: "load", mem: this.mem });
 		this.worker.onmessage = (e) => {
 			clearInterval(dots);
 			this.print(" done\n");
+			this.worker.postMessage({ type: "boot" });
 		};
 
 		fetch('prelude.f')