Added encoding support for decimal objects

tests/test_json.py

@@ -1,4 +1,5 @@
 import datetime
+import decimal
 import io
 import uuid
 
@@ -9,6 +10,11 @@ import flask
 from flask import json
 
 
+def test_json_encode_decimal():
+    decimal_ = decimal.Decimal(100)
+    assert flask.json.JSONEncoder().default(decimal_) == str(decimal_)
+
+
 @pytest.mark.parametrize("debug", (True, False))
 def test_bad_request_debug_message(app, client, debug):
     app.config["DEBUG"] = debug