Update specs example to use new types (without "string/" prefix)

Follows-up 6cdb47d097543d88d58e0 which dropped the prefixes. The example
was still using 'string/wiki-user-name' instead of 'wiki-user-name'.

Change-Id: Ia6f353600cea6e3da53ea0cabc45a77d35642e40
Merge "Update specs example to use new types (without "string/" prefix)"