Clean Buidler cache before publishing

package.json

@@ -19,7 +19,7 @@
     "lint:js": "eslint --ignore-path .gitignore .",
     "lint:js:fix": "eslint --ignore-path .gitignore . --fix",
     "lint:sol": "solhint --max-warnings 0 \"contracts/**/*.sol\"",
-    "prepublish": "rimraf build contracts/build artifacts",
+    "prepublish": "rimraf build contracts/build artifacts cache",
     "prepare": "npm run compile",
     "prepack": "scripts/prepack.sh",
     "release": "scripts/release/release.sh",