Parsed strings retain quotes

Given `"rename GO:1 from 'foo' to 'bar'"`

the parser returns

```jjson
{
  "id": "CHANGE:001",
  "old_value": "'foo'",
  "new_value": "'bar'",
  "about_node": "GO:1",
  "about_node_representation": "curie",
  "@type": "NodeRename"
} 
```

The quoted value is itself quoted