get rid of postpublish script

Author: jedwards1211

package.json

@@ -31,7 +31,6 @@
     "build": "rimraf lib && babel src --out-dir lib",
     "test": "NODE_ENV=production BABEL_ENV=test nyc --reporter=lcov --reporter=text mocha $npm_package_config_mocha",
     "prepublish": "npm run lint && flow && npm test && npm run build && npm run copy-flow-files",
-    "postpublish": "git tag -a v$npm_package_version -m v$npm_package_version && git push origin v$npm_package_version",
     "open:coverage": "open coverage/lcov-report/index.html",
     "semantic-release": "semantic-release pre && npm publish && semantic-release post"
   },