Use cross-env to run tests (codesandbox#2916)

This lets `yarn test` work on Windows (without installing something like `win-node-env`).

Author: stevetaggart

packages/common/package.json

@@ -20,7 +20,7 @@
     "prepublish": "yarn build",
     "start": "(yarn tsc --watch & yarn babel src --out-dir lib --watch & yarn cpx \"src/**/*.{css,svg,png,jpg}\" lib --watch)",
     "start:storybook": "start-storybook",
-    "test": "NODE_ENV=test jest",
+    "test": "cross-env NODE_ENV=test jest",
     "typecheck": "tsc --noEmit"
   },
   "jest": {