test: run clean before test instead of after

Author: yyx990803

package.json

@@ -6,7 +6,7 @@
   ],
   "scripts": {
     "test": "node scripts/test.js",
-    "posttest": "yarn clean",
+    "pretest": "yarn clean",
     "lint": "eslint --fix packages/**/*.js packages/**/bin/* test/**/*.js",
     "clean": "rimraf packages/test/*",
     "sync": "node scripts/syncDeps.js",