title: Django Rest Framework - Serializer Method field
body: <p>When using serializer method field, the dictionary with Decimals is converted to Integers.</p>
  
  <p>For eg.</p>
  
  <pre><code>class BillSerializer(serializers.ModelSerializer):
      bill_details = serializers.SerializerMethodField()
  
      class Meta:
          model = Bill
          fields = ('__all__')
  
      def get_bill_details(obj):
          return {'editable': False,
             'final_amt': Decimal('4198.00'),
             'total_amt': Decimal('4198.00'),
          }
  </code></pre>
  
  <p>becomes this:</p>
  
  <pre><code>"bill_details": {
      "total_amt": 4198,
      "editable": false,
      "final_amt": 4198
    }
  </code></pre>
  
  <p>Is there any solution to this? I am expecting this:</p>
  
  <pre><code>"bill_details": {
      "total_amt": "4198.00",
      "editable": false,
      "final_amt": "4198.00"
  }
  </code></pre>