Limit worker pool size (microsoft#185164)

Fixes microsoft#185079

Should fix OOM issues on build machines

Author: mjbvz

build/lib/mangle/index.js

@@ -416,7 +416,7 @@ export class Mangler {
 		this.service = ts.createLanguageService(new StaticLanguageServiceHost(projectPath));
 
 		this.renameWorkerPool = workerpool.pool(path.join(__dirname, 'renameWorker.js'), {
-			maxWorkers: 2,
+			maxWorkers: 1,
 			minWorkers: 'max'
 		});
 	}