Update cross-env to the latest version 🚀 (#431)

* chore(package): update cross-env to version 4.0.0

https://greenkeeper.io/

* yarn.lock

package.json

@@ -28,7 +28,7 @@
     "babel-preset-env": "^1.2.0",
     "babel-register": "^6.18.0",
     "codecov": "^1.0.1",
-    "cross-env": "^3.1.4",
+    "cross-env": "^4.0.0",
     "eslint": "^3.8.1",
     "eslint-config-babel": "^6.0.0",
     "eslint-plugin-flowtype": "^2.25.0",

yarn.lock

@@ -1346,9 +1346,9 @@ create-hmac@^1.1.0, create-hmac@^1.1.2:
     create-hash "^1.1.0"
     inherits "^2.0.1"
 
-cross-env@^3.1.4:
-  version "3.2.3"
-  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-3.2.3.tgz#a43a0799b8ec422d0279b829ce8d7cf2da6b17ac"
+cross-env@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-4.0.0.tgz#16083862d08275a4628b0b243b121bedaa55dd80"
   dependencies:
     cross-spawn "^5.1.0"
     is-windows "^1.0.0"