Fix aria-level allowed on elements wit role heading (#704)

Author: jessebeach

__tests__/src/rules/role-supports-aria-props-test.js

@@ -381,6 +381,8 @@ ruleTester.run('role-supports-aria-props', rule, {
     { code: '<textarea aria-hidden />' },
     { code: '<select aria-expanded />' },
     { code: '<datalist aria-expanded />' },
+    { code: '<div role="heading" aria-level />'},
+    { code: '<div role="heading" aria-level="1" />'}
 
   ].concat(validTests).map(parserOptionsMapper),