Update cross-env to the latest version 🚀 (#443)

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

https://greenkeeper.io/

* Update yarn.lock

package.json

@@ -31,7 +31,7 @@
     "babel-preset-es2015": "^7.0.0-alpha.3",
     "babel-preset-stage-0": "^7.0.0-alpha.3",
     "chalk": "^1.1.3",
-    "cross-env": "^3.1.4",
+    "cross-env": "^4.0.0",
     "eslint": "^3.7.1",
     "eslint-config-babel": "^6.0.0",
     "eslint-plugin-flowtype": "^2.20.0",

yarn.lock

@@ -1510,9 +1510,9 @@ create-error-class@^3.0.1:
   dependencies:
     capture-stack-trace "^1.0.0"
 
-cross-env@^3.1.4:
-  version "3.2.4"
-  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-3.2.4.tgz#9e0585f277864ed421ce756f81a980ff0d698aba"
+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"