Fix package.json for prepublish scripts are deprecated in npm@5.

Author: jackycute

package.json

@@ -10,7 +10,7 @@
   "scripts": {
     "build": "./node_modules/.bin/rollup -c",
     "watch": "./node_modules/.bin/rollup -w -c",
-    "prepublish": "npm run-script build",
+    "prepare": "npm run-script build",
     "test": "node ./test/run.js",
     "lint": "bin/lint",
     "install": "npm run-script build && ./release.sh"