test: change prod-build E2E bootstrap check to allow underscore in variable name

Author: clydin

tests/legacy-cli/e2e/tests/build/prod-build.ts

@@ -27,7 +27,7 @@ export default async function () {
 
   // Can't use the `ng` helper because somewhere the environment gets
   // stuck to the first build done
-  const bootstrapRegExp = /bootstrapModule\([a-zA-Z]+[0-9]*\)\./;
+  const bootstrapRegExp = /bootstrapModule\([_a-zA-Z]+[0-9]*\)\./;
 
   await noSilentNg('build');
   await expectFileToExist(join(process.cwd(), 'dist'));