prepublish -> prepare

Fix npm deprecation warning

package.json

@@ -61,7 +61,7 @@
   },
   "scripts": {
     "build": "mkdir -p dist && babel src/cmd.js > dist/cmd.js && chmod +x dist/cmd.js",
-    "prepublish": "npm run build",
+    "prepare": "npm run build",
     "test": "standard && npm run build && ./dist/cmd.js --no-open"
   }
 }