try to adapt package.json for heroku

Author: tuxcy17

package.json

@@ -2,6 +2,7 @@
   "name": "sandbox-angular4",
   "version": "0.0.0",
   "license": "MIT",
+  "main": "server.js",
   "scripts": {
     "ng": "ng",
     "start": "ng serve",
@@ -10,10 +11,17 @@
     "lint": "ng lint",
     "package": "ng build --aot -prod",
     "prod": "npm run package ; node server.js",
-    "e2e": "ng e2e"
+    "e2e": "ng e2e",
+    "postinstall": "ng build --aot -prod"
+  },
+  "engines": {
+    "node": "~7.10.0",
+    "npm": "~4.2.0"
   },
   "private": true,
   "dependencies": {
+    "@angular/cli": "1.3.0",
+    "@angular/compiler-cli": "^4.2.4",
     "@angular/animations": "^4.2.4",
     "@angular/common": "^4.2.4",
     "@angular/compiler": "^4.2.4",
@@ -29,8 +37,6 @@
     "zone.js": "^0.8.14"
   },
   "devDependencies": {
-    "@angular/cli": "1.3.0",
-    "@angular/compiler-cli": "^4.2.4",
     "@angular/language-service": "^4.2.4",
     "@types/jasmine": "~2.5.53",
     "@types/jasminewd2": "~2.0.2",