Update the library tests after bug in RDF4J gets fixed

[svilenvelikov]

Following MR #96 hit a bug in RDF4J version used in the GraphDB 9.4.0. and we had to change the tests to account the actual "broken" response.

We should watch the related issue in RDF4J and when it gets fixed and enters in a GDB release, we must update the tests respectively and release the library as well.

[teodossidossev]

Tests should fail again when functionality is fixed and we upgrade GDB version