chore(publish): add prepare hook (#108)

Add [`prepare`](https://docs.npmjs.com/misc/scripts) hook to automatically test and build before publishing.

Author: Tyler Brandt

packages/optimizely-sdk/package.json

@@ -18,7 +18,8 @@
     "build-prod-umd": "webpack -p lib/index.browser.js dist/optimizely.browser.umd.min.js --output-library=optimizelyClient --output-library-target=umd",
     "lint": "eslint lib/**",
     "cover": "istanbul cover _mocha ./lib/*.tests.js ./lib/**/*.tests.js ./lib/**/**/*tests.js",
-    "coveralls": "npm run cover -- --report lcovonly && cat ./coverage/lcov.info | coveralls"
+    "coveralls": "npm run cover -- --report lcovonly && cat ./coverage/lcov.info | coveralls",
+    "prepare": "npm test && npm run build"
   },
   "repository": {
     "type": "git",