fix(package): make library npm link friendly

Author: webmaxru

package.json

@@ -2,10 +2,11 @@
   "name": "angularfire2",
   "version": "2.0.0-alpha.6",
   "description": "",
-  "main": "angularfire.js",
+  "main": "./dist/angularfire.js",
   "scripts": {
     "test": "npm run build; karma start",
     "build": "rm -rf dist; tsc && cp package.json README.md LICENSE .npmignore dist/",
+    "postbuild": "./node_modules/.bin/json -I -f ./dist/package.json -e 'this.main=\"angularfire.js\"'",
     "install_webdriver": "webdriver-manager update",
     "install_typings": "typings install"
   },
@@ -38,14 +39,15 @@
     "http-server": "^0.8.5",
     "jasmine": "^2.4.1",
     "jasmine-core": "^2.4.1",
+    "json": "^9.0.3",
     "karma": "^0.13.19",
     "karma-chrome-launcher": "^0.2.2",
     "karma-firefox-launcher": "^0.1.7",
     "karma-jasmine": "^0.3.6",
     "karma-systemjs": "^0.10.0",
     "parse5": "^1.3.2",
     "protractor": "3.0.0",
-    "reflect-metadata": "^0.1.2",
+    "reflect-metadata": "0.1.2",
     "systemjs": "^0.19.16",
     "traceur": "0.0.96",
     "tsd": "^0.6.5",