Update release script to install firebase-admin (#16)

Author: laurenzlong

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "build": "npm i && node_modules/.bin/tsc -p tsconfig.release.json",
     "build:pack": "npm prune --production && rm -rf lib && npm install && node_modules/.bin/tsc -p tsconfig.release.json && npm pack && npm install",
-    "build:release": "npm install --production && npm install typescript firebase-functions && node_modules/.bin/tsc -p tsconfig.release.json",
+    "build:release": "npm install --production && npm install typescript firebase-functions firebase-admin && node_modules/.bin/tsc -p tsconfig.release.json",
     "lint": "node_modules/.bin/tslint src/{**/*,*}.ts spec/{**/*,*}.ts",
     "pretest": "node_modules/.bin/tsc",
     "test": "mocha .tmp/spec/index.spec.js",