Feature: Get the correct type for skos concepts

[syphax-bouazzouni]

Issue

If we take as an example the NLMVS ontology, which is SKOS terminology with only SKOS Concepts (no OWL ontology)

But when we check one of its concepts like Intraspinal abscess (disorder) , our API tell us that is of @type: "owl:Class" (see screenshot below)

This PR fix that, by displaying the correct type, skos:Concept if SKOS and owl:Class if Ontology

After

[codecov]

Codecov Report

Merging #162 (81c7977) into master (b5057b4) will decrease coverage by 0.02%.
The diff coverage is 70.00%.

❗ Current head 81c7977 differs from pull request most recent head ba7a7f8. Consider uploading reports for the commit ba7a7f8 to get more accurate results

@@            Coverage Diff             @@
##           master     #162      +/-   ##
==========================================
- Coverage   80.75%   80.72%   -0.03%     
==========================================
  Files          63       63              
  Lines        4848     4857       +9     
==========================================
+ Hits         3915     3921       +6     
- Misses        933      936       +3     

Flag	Coverage Δ
unittests	80.72% <70.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
lib/ontologies_linked_data/serializers/json.rb	79.22% <70.00%> (-1.67%)	⬇️

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[alexskr]

already implemented via PR #199 36a5b68