fix(build): Add package.json files for deep paths

Closes angular#880

Author: cartant

src/app/package.json

@@ -0,0 +1 @@
+{ "main": "../bundles/angularfire2.umd.js" }

src/auth/package.json

@@ -0,0 +1 @@
+{ "main": "../bundles/angularfire2.umd.js" }

src/database/package.json

@@ -0,0 +1 @@
+{ "main": "../bundles/angularfire2.umd.js" }

tools/rewrite-published-package.js

@@ -15,3 +15,10 @@ delete srcPackage.dependencies;
 var outPackage = Object.assign({}, srcPackage, { peerDependencies });
 
 fs.writeFileSync('./dist/package.json', JSON.stringify(outPackage, null, 2));
+
+// It's also necessary to copy any deep-path package.json files.
+// See https://github.com/angular/angularfire2/issues/880
+
+['app', 'auth', 'database'].forEach(dir => {
+  fs.writeFileSync(`./dist/${dir}/package.json`, fs.readFileSync(`./src/${dir}/package.json`));
+});