title: Graphene: Enum argument doesn't seem to work
body: <p>Im currently having hard time on mutation enum <code>Argument</code>.</p>
  
  <p>Below are my code for <code>Mutation</code>:</p>
  
  <pre><code>class CreatePerson(graphene.Mutation):
      foo = graphene.String()
  
      def mutate(self, info, **kwargs):
          return CreatePerson(foo='foo')
  
  
      class Arguments:
          enum_arg = graphene.Argument(graphene.Enum.from_enum(EnumArg))
  </code></pre>
  
  <p>Enum class:</p>
  
  <pre><code>from enum import Enum
  
  class EnumArg(Enum):
      Baz = 0
      Bar = 1
      Spam = 2
      Egg = 3
  </code></pre>
  
  <p>Command using <strong>POSTMAN</strong>:</p>
  
  <pre><code>{
      "query": "mutation": {createPerson(enumArg=1) { foo }}
  }
  </code></pre>
  
  <p>But I end up this error message:</p>
  
  <pre><code>"message": "Argument \"enumArg\" has invalid value 1.
              Expected type \"EnumArg\", found 1.",
  </code></pre>
  
  <p>I also tried giving <code>enumArg=\"Bar\"</code> on the <code>createPerson</code> mutation and the error still persists.</p>