chore: Use cross-env in npm scripts; closes #167 (#168)

Also updates yarn.lock to reflect dependency versions in package.json

Author: bertday

package.json

@@ -8,10 +8,10 @@
     "test": "npm run lint && npm run build && npm run unit",
     "build": "node config/build.js",
     "dev": "npm run unit -- -w",
-    "unit": "NODE_ENV=production mocha test/test.js --slow=5000 --timeout=10000",
+    "unit": "cross-env NODE_ENV=production mocha test/test.js --slow=5000 --timeout=10000",
     "lint": "eslint src/**",
     "lint:fix": "eslint --fix src/**",
-    "coveralls": "NODE_ENV=production istanbul cover --default-excludes -x 'dist/**' -x 'config/**' ./node_modules/mocha/bin/_mocha --report lcovonly  --  --slow=5000 --timeout=10000 test/test.js && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js && rm -rf ./coverage",
+    "coveralls": "cross-env NODE_ENV=production istanbul cover --default-excludes -x 'dist/**' -x 'config/**' ./node_modules/mocha/bin/_mocha --report lcovonly  --  --slow=5000 --timeout=10000 test/test.js && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js && rm -rf ./coverage",
     "prepare": "npm run build",
     "docs": "php -S localhost:8080 -t .github/sereno/public"
   },
@@ -62,6 +62,7 @@
     "babel-preset-stage-2": "^6.22.0",
     "clean-css": "^3.4.24",
     "coveralls": "^2.11.15",
+    "cross-env": "^5.1.3",
     "eslint": "^3.14.0",
     "eslint-config-standard": "^6.2.1",
     "eslint-plugin-html": "^1.7.0",