Add tests that show that with nullable option on but 'nullable' keyword set to false an object is not nullable.

spec/options.spec.js

@@ -1519,6 +1519,18 @@ describe('Ajv Options', function () {
 
         testNotNullable({type: ['number']});
       });
+      
+      it('should respect "nullable" == false with opts.nullable == true', function() {
+        testNotNullable({
+          type: 'number',
+          nullable: false
+        });
+
+        testNotNullable({
+          type: ['number'],
+          nullable: false
+        });
+      });
     });
 
     describe('without option "nullable"', function() {