🏁 Cross-platform build npm script (#85)

* 🔧 normalize package-lock.json

This is what package-lock.json looks like after a clean clone and npm install with npm 5.3.0.

* 🏁 cross-platform build command

package.json

@@ -27,6 +27,7 @@
     "babel-preset-env": "^1.6.0",
     "babel-preset-stage-2": "^6.24.1",
     "codecov": "^2.3.0",
+    "cross-env": "^5.0.5",
     "eslint": "^4.4.1",
     "hotdoc": "^0.7.2",
     "jest": "^20.0.4",
@@ -36,7 +37,7 @@
     "lodash": "^4.17.4"
   },
   "scripts": {
-    "build": "BABEL_ENV=production babel src -d .",
+    "build": "cross-env BABEL_ENV=production babel src -d .",
     "lint": "eslint src misc",
     "test": "jest",
     "test:coverage": "jest --coverage && codecov",

yarn.lock

@@ -1218,6 +1218,13 @@ core-util-is@~1.0.0:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/core-util-is/-/core-util-is-1.0.2.tgz#b5fd54220aa2bc5ab57aab7140c940754503c1a7"
 
+cross-env@^5.0.5:
+  version "5.0.5"
+  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-5.0.5.tgz#4383d364d9660873dd185b398af3bfef5efffef3"
+  dependencies:
+    cross-spawn "^5.1.0"
+    is-windows "^1.0.0"
+
 cross-spawn@^3.0.0:
   version "3.0.1"
   resolved "https://registry.yarnpkg.com/cross-spawn/-/cross-spawn-3.0.1.tgz#1256037ecb9f0c5f79e3d6ef135e30770184b982"
@@ -2208,6 +2215,10 @@ is-utf8@^0.2.0:
   version "0.2.1"
   resolved "https://registry.yarnpkg.com/is-utf8/-/is-utf8-0.2.1.tgz#4b0da1442104d1b336340e80797e865cf39f7d72"
 
+is-windows@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/is-windows/-/is-windows-1.0.1.tgz#310db70f742d259a16a369202b51af84233310d9"
+
 isarray@1.0.0, isarray@^1.0.0, isarray@~1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/isarray/-/isarray-1.0.0.tgz#bb935d48582cba168c06834957a54a3e07124f11"