WShEx: couple fixes to spec

[VladimirAlexiev]

@labra A couple of suggestions for https://www.weso.es/WShEx/ (can't find a repo for that spec, so posting here:

• Don't give a recursive example shape in Researcher: @<Researcher>. Even if recursive shapes are allowed in ShEx, this leads to uncontrollable expansion of checking work. Eg Researcher->n*Awards-m*Researchers-p*Awards will lead to expansion of n+n*m+n*m*p checks, and that's not all
• misspelling "slach"
• https://www.weso.es/WShEx/#Sitelinks seems incomplete to me (a shortcut that's become "too short").
  Eg https://www.wikidata.org/wiki/Special:EntityData/Q42.ttl has multiple "en" about links, here are shown two (wikipedia and wikiquote). How can I check for one or another:

<https://en.wikipedia.org/wiki/Douglas_Adams> a schema:Article ;
	schema:about wd:Q42 ;
	schema:inLanguage "en" ;
	schema:isPartOf <https://en.wikipedia.org/> ;
	schema:name "Douglas Adams"@en .

<https://en.wikipedia.org/> wikibase:wikiGroup "wikipedia" .

<https://en.wikiquote.org/wiki/Douglas_Adams> a schema:Article ;
	schema:about wd:Q42 ;
	schema:inLanguage "en" ;
	schema:isPartOf <https://en.wikiquote.org/> ;
	schema:name "Douglas Adams"@en .

<https://en.wikiquote.org/> wikibase:wikiGroup "wikiquote" .