rename prebuild to clean

npm sometimes fail to run prebuild before build. Using clean makes it 
explicit

Author: aminya

package.json

@@ -6,8 +6,8 @@
   "main": "dist/index.js",
   "module": "dist-esm/index.js",
   "scripts": {
-    "prebuild": "rimraf dist/ dist-esm/",
-    "build": "npm run build:cjs && npm run build:es",
+    "clean": "rimraf dist/ dist-esm/",
+    "build": "npm run clean && npm run build:cjs && npm run build:es",
     "build:cjs": "tsc -p tsconfig.json",
     "build:es": "tsc -p tsconfig-esm.json",
     "postbuild": "npm run bundle",