build: filter out changelog entries for zone.js from framework changelog (#31277)

We don't want to show entries for the `zone.js` scope in the main framework
changelog file. The zone.js changelog will be handled separately within the
`packages/zone.js` folder. (see [here](https://github.com/angular/angular/pull/31277#issuecomment-505934681))

PR Close #31277

tools/gulp-tasks/changelog.js

@@ -12,6 +12,7 @@ module.exports = (gulp) => () => {
     'aio',
     'docs-infra',
     'ivy',
+    'zone.js',
   ];
 
   return gulp.src('CHANGELOG.md')