Ensure package is published from dist/ with correct version number (#2963)

package.json

@@ -72,6 +72,7 @@
     "webpack": "2.6.1"
   },
   "scripts": {
+    "prepublishOnly": "echo \"Error: must publish from dist/\" && exit 1",
     "test": "jest",
     "test-integration": "jest tests_integration",
     "lint": "cross-env EFF_NO_LINK_RULES=true eslint . --format node_modules/eslint-friendly-formatter",

scripts/build/build.js

@@ -123,6 +123,10 @@ shell.cp("node_modules/sw-toolbox/sw-toolbox.js", `${docs}/sw-toolbox.js`);
 shell.echo("Copy package.json");
 const pkgWithoutDependencies = Object.assign({}, pkg);
 delete pkgWithoutDependencies.dependencies;
+pkgWithoutDependencies.scripts = {
+  prepublishOnly:
+    "node -e \"assert.equal(require('.').version, require('..').version)\""
+};
 pipe(JSON.stringify(pkgWithoutDependencies, null, 2)).to("dist/package.json");
 
 shell.echo("Copy README.md");