datepicker: updated test case to be more specific to the use case

Author: jigar140291

tests/unit/datepicker/methods.js

@@ -17,7 +17,7 @@ QUnit.test( "destroy", function( assert ) {
 	inp.datepicker( "show" );
 	assert.equal( dp.css( "display" ), "block", "Datepicker - visible" );
 	inp.datepicker( "hide" ).datepicker( "destroy" );
-	assert.ok( !$.datepicker._curInst, "Datepicker - destroyed and cleared reference" );
+	assert.ok( $.datepicker._curInst == null, "Datepicker - destroyed and cleared reference" );
 
 	inp = testHelper.init( "#inp" );
 	assert.ok( inp.is( ".hasDatepicker" ), "Default - marker class set" );