Errors in go meta_schema package

**Describe the bug**
Too many errors in go meta schema (Undefined: Undefined)

**To Reproduce**
1. Go to https://github.com/open-rpc/meta-schema/blob/master/openrpc_document.go#L170

**Expected behavior**
I tried to use it as a dependency but I can't

**Additional context**
Add any other context about the problem here.
