Fix small errors in intro-to-linked-data

[charlottejmc]

While working on the FR translation of en/intro-to-linked-data, the translator (our project team member @davvalent) noticed a few errors which should be corrected. I'm copying them over from his comment:

• Code snippet following ¶55: The final slash in the URI is strictly necessary, so it should be http://data.history.ac.uk/tobias-project/person/, not http://data.history.ac.uk/tobias-project/person. Otherwise an RDF parser would resolve to http://data.history.ac.uk/tobias-project/person15601, which is nothing
• Code snippet following ¶57:
  • The final slash in the URI is strictly necessary, so it should be http://id.loc.gov/authorities/names/, not http://id.loc.gov/authorities/names.
  • Same for http://viaf.org/viaf <-- final slash needed
• Code snippet following ¶60: same as above
• ¶76: It should be "SPARQL Protocol and RDF Query Language" (lacks RDF).
• ¶78 : The link on DBpedia should be https://en.wikipedia.org/wiki/DBpedia, not https://en.wikipedia.org/wiki/SPARQL
• ¶86: “Note that here, searching for a string, case does matter: lyndal_roper will get you no results.”
  • It's true that case does matter here, but we're not seaching for a string, stricto sensu, since this is an IRI, not a literal, in the RDF term syntax as defined in the SPARQL 1.1 Standard. This is a fundamental distinction to be made when learning RDF and SPARQL. Therefore I suggest simply removing the “searching for a string” part.
• ¶90: “I use ?a and ?b” --> Should be ?b and ?c in order to be consistent with the code snippets.
• ¶98 : “by asking a for a variable” --> by asking for a variable

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I'll also check whether these need to be corrected in the PT and ES translations.