build: use prepublish instead of prepack

Author: dead-horse

.travis.yml

@@ -14,7 +14,6 @@ before_script:
   - export PATH=$PATH:$PWD/wrk/bin/
 script:
   - npm run lint
-  - npm run prepack
   - npm run test-cov
   - npm run bench
 after_script:

package.json

@@ -17,7 +17,7 @@
     "bench": "make -C benchmarks",
     "authors": "git log --format='%aN <%aE>' | sort -u > AUTHORS",
     "build": "gen-esm-wrapper . ./dist/koa.mjs",
-    "prepack": "npm run build"
+    "prepublish": "npm run build"
   },
   "repository": "koajs/koa",
   "keywords": [