build(package): update build:min to generate sourcemap (external)

Author: remarkablemark

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "build": "npm run clean && npm run build:min && npm run build:unmin",
-    "build:min": "NODE_ENV=production rollup --config --output.file dist/inline-style-parser.min.js",
+    "build:min": "NODE_ENV=production rollup --config --output.file dist/inline-style-parser.min.js --sourcemap",
     "build:unmin": "rollup --config --file dist/inline-style-parser.js",
     "clean": "rm -rf dist",
     "coveralls": "cat coverage/lcov.info | coveralls",