chore: add cross-env to scripts for cross platform support (#23)

package.json

@@ -21,6 +21,7 @@
     "babel-plugin-transform-export-extensions": "^6.8.0",
     "babel-register": "^6.18.0",
     "chai": "^3.5.0",
+    "cross-env": "^3.1.3",
     "eslint": "^3.9.1",
     "eslint-config-canonical": "^4.0.0",
     "husky": "^0.11.9",
@@ -43,11 +44,11 @@
     "url": "https://github.com/gajus/create-index"
   },
   "scripts": {
-    "build": "NODE_ENV=production babel --source-maps --copy-files ./src --out-dir ./dist",
+    "build": "cross-env NODE_ENV=production babel --source-maps --copy-files ./src --out-dir ./dist",
     "create-index": "node ./dist/bin/create-index ./src/utilities",
-    "lint": "NODE_ENV=development eslint ./src ./tests",
+    "lint": "cross-env NODE_ENV=development eslint ./src ./tests",
     "precommit": "npm run test",
-    "test": "npm run build && npm run lint && NODE_ENV=development mocha --compilers js:babel-register"
+    "test": "npm run build && npm run lint && cross-env NODE_ENV=development mocha --compilers js:babel-register"
   },
   "version": "1.1.0"
 }