fix(package): Add source-map files to npm releases (#4206)

Author: Pavel Sevcik

scripts/cp-pkgs.js

@@ -79,7 +79,7 @@ function cpAsset(asset) {
 
 cleanPkgDistDirs();
 
-Promise.all(globSync('build/*.{css,js}').map(cpAsset)).catch((err) => {
+Promise.all(globSync('build/*.{css,js,map}').map(cpAsset)).catch((err) => {
   console.error(`Error encountered copying assets: ${err}`);
   process.exit(1);
 });