PR: Upgrade ujson dependency

setup.py

@@ -1,10 +1,21 @@
 #!/usr/bin/env python
 from setuptools import find_packages, setup
+import sys
 import versioneer
 
 README = open('README.rst', 'r').read()
 
 
+install_requires = [
+    'future>=0.14.0; python_version<"3"',
+    'futures; python_version<"3.2"',
+]
+
+if sys.version_info[0] == 2:
+    install_requires.append('ujson<=2.0.3; platform_system!="Windows"')
+else:
+    install_requires.append('ujson>=3.0.0')
+
 setup(
     name='python-jsonrpc-server',
 
@@ -31,11 +42,7 @@
     # your project is installed. For an analysis of "install_requires" vs pip's
     # requirements files see:
     # https://packaging.python.org/en/latest/requirements.html
-    install_requires=[
-        'future>=0.14.0; python_version<"3"',
-        'futures; python_version<"3.2"',
-        'ujson<=1.35; platform_system!="Windows"',
-    ],
+    install_requires=install_requires,
 
     # List additional groups of dependencies here (e.g. development
     # dependencies). You can install these using the following syntax,

test/test_streams.py

@@ -1,7 +1,9 @@
 # Copyright 2018 Palantir Technologies, Inc.
 # pylint: disable=redefined-outer-name
 from io import BytesIO
+import datetime
 import os
+import sys
 import mock
 import pytest
 
@@ -95,11 +97,21 @@ def test_writer(wfile, writer):
         )
 
 
+class JsonDatetime(datetime.datetime):
+    """Monkey path json datetime."""
+    def __json__(self):
+        if sys.version_info.major == 3:
+            dif = int(self.timestamp())
+        else:
+            dif = int((self - datetime.datetime(1970, 1, 1)).total_seconds())
+        return '{0}'.format(dif)
+
+
 def test_writer_bad_message(wfile, writer):
     # A datetime isn't serializable(or poorly serializable),
     # ensure the write method doesn't throw, but the result could be empty
     # or the correct datetime
-    import datetime
+    datetime.datetime = JsonDatetime
     writer.write(datetime.datetime(
         year=2019,
         month=1,