Confirm compatibility with Node 8.x

lib/cluster.js

@@ -27,7 +27,7 @@ const VERSION = require("../package.json").version;
 function getDependencyVersions() {
   let dependencies = [`node@${process.versions.node}`];
   try {
-    let npmls = JSON.parse(require("child_process").execSync("npm ls --prod --json"));
+    let npmls = JSON.parse(require("child_process").execSync("npm ls --prod --json --depth 0"));
 
     for (let k in npmls.dependencies)
       dependencies.push(`${k}@${npmls.dependencies[k].version}`);