neo4j: update expected test results with full serialized objects

Signed-off-by: Alexis Laferrière <[email protected]>

lib/neo4j/error.nit

@@ -17,7 +17,7 @@ import json::serialization
 # An error thrown by the `neo4j` API.
 #
 #     var error = new NeoError("ErrorMessage", "ErrorName")
-#     assert error.to_json == "\{\"error\":\"ErrorName\",\"message\":\"ErrorMessage\"\}"
+#     assert error.to_json == """{"message":"ErrorMessage","cause":null,"error":"ErrorName"}"""
 class NeoError
 	super Error
 	super Jsonable