smoke - fix compile error

test/smoke/src/spectron/client.ts

@@ -14,7 +14,7 @@ export class SpectronClient {
 
 	// waitFor calls should not take more than 200 * 100 = 20 seconds to complete, excluding
 	// the time it takes for the actual retry call to complete
-	private readonly retryCount;
+	private retryCount: number;
 	private readonly retryDuration = 100; // in milliseconds
 
 	constructor(public spectron: Application, private application: SpectronApplication) {