Update dotenv to 5.0.0 (facebook#4009)

Author: iansu

package.json

@@ -33,7 +33,7 @@
     "case-sensitive-paths-webpack-plugin": "2.1.1",
     "chalk": "2.3.0",
     "css-loader": "0.28.9",
-    "dotenv": "4.0.0",
+    "dotenv": "5.0.0",
     "dotenv-expand": "4.2.0",
     "eslint": "4.15.0",
     "eslint-config-react-app": "^2.1.0",