Add ChromeOS support in defaultPlatform frontmatter (#4102)

* Add ChromeOS support

Adds CrOS to defaultPlatform frontmatter, as Linux.

* Update schema-event.js

* Update schema-event.js

Co-authored-by: Kevin Heis <heiskr@users.noreply.github.com>

lib/schema-event.js

@@ -73,7 +73,7 @@ const context = {
     os: {
       type: 'string',
       description: 'The type of operating system the user is working with.',
-      enum: ['windows', 'mac', 'linux', 'ios', 'android', 'other'],
+      enum: ['windows', 'mac', 'linux', 'ios', 'android', 'cros', 'other'],
       default: 'other'
     },
     os_version: {