test: use spread instead of Object.assign

Author: dnlup

test/benchmark/test-benchmark-dns.js

@@ -4,7 +4,6 @@ require('../common');
 
 const runBenchmark = require('../common/benchmark');
 
-const env = Object.assign({}, process.env,
-                          { NODEJS_BENCHMARK_ZERO_ALLOWED: 1 });
+const env = { ...process.env, NODEJS_BENCHMARK_ZERO_ALLOWED: 1 };
 
 runBenchmark('dns', ['n=1', 'all=false', 'name=127.0.0.1'], env);