feat(angular-cli): Add a postinstall warning for Node 4 deprecation.

BREAKING CHANGE: Node < 6.9 will be deprecated soon, and this will show a warning to users. Moving forward, that warning will be moved to an error with the next release.

packages/angular-cli/package.json

@@ -19,6 +19,9 @@
     "node": ">= 4.1.0",
     "npm": ">= 3.0.0"
   },
+  "scripts": {
+    "postinstall": "node ./scripts/install.js"
+  },
   "author": "Angular Authors",
   "license": "MIT",
   "bugs": {

packages/angular-cli/scripts/install.ts

@@ -0,0 +1,23 @@
+#!/usr/bin/env node
+/* eslint-disable no-console */
+import {stripIndent} from 'common-tags';
+import {yellow} from 'chalk';
+
+const SemVer = require('semver').SemVer;
+
+const version = new SemVer(process.version);
+if (version.compare('6.9.0') < 0) {
+  console.log(yellow(stripIndent`
+    We detected that you are using Node v${version.version}. Unfortunately, this version will not
+    be officially supported when the Angular CLI is released. The official Node version that will
+    be supported is 6.9 and greater. This beta release (Beta.27) will be the last release to
+    support Node 4.
+
+    This is to ensure that we can provide our users with better support for the upcoming releases.
+    Many of our dependencies are moving to deprecating Node 4 already and that would mean that we
+    could not update them to the latest versions which might have bug fixes and new useful features.
+
+    As a forewarning, We are also moving to "@angular/cli" with the next release, which will only
+    support Node 6.9 and greater. This package will be officially deprecated shortly after.
+  `));
+}