Create npm script clean that removes dist/ directory

Rename `build` to `build-unmin` and update `prepublish` to run
`clean` before the build scripts.

Author: remarkablemark

package.json

@@ -5,9 +5,10 @@
   "author": "Mark <mark@remarkablemark.org>",
   "main": "index.js",
   "scripts": {
-    "build": "NODE_ENV=development webpack index.js dist/html-react-parser.js",
+    "build-unmin": "NODE_ENV=development webpack index.js dist/html-react-parser.js",
     "build-min": "NODE_ENV=production webpack -p index.js dist/html-react-parser.min.js",
-    "prepublish": "npm run build && npm run build-min",
+    "clean": "rm -rf dist",
+    "prepublish": "npm run clean && npm run build-unmin && npm run build-min",
     "test": "mocha",
     "lint": "eslint index.js \"lib/**\" \"test/**\"",
     "cover": "istanbul cover _mocha -- -R spec \"test/**/*\"",