Add snapshot testing

Author: simeg

package.json

@@ -22,8 +22,10 @@
     "dev": "./node_modules/.bin/webpack-dev-server --config example/webpack.config.js --devtool eval --progress --colors --hot --content-base example",
     "lint": "./node_modules/.bin/eslint src/ DateTime.js test/",
     "test": "./node_modules/.bin/jest",
-    "test:all": "npm run test:typings && npm run test",
     "test:typings": "./node_modules/.bin/tsc -p ./typings",
+    "test:snapshot": "./node_modules/.bin/jest snapshot",
+    "test:snapshot:update": "./node_modules/.bin/jest snapshot --updateSnapshot",
+    "test:all": "npm run test:typings && npm run test",
     "test:watch": "./node_modules/.bin/jest --watch"
   },
   "keywords": [