Use unittest.mock instead of mock

Closes #62.

Makefile

@@ -27,7 +27,7 @@ include release.mk
 
 
 bin/pytest: | bin/pip
-	bin/pip install pytest mock
+	bin/pip install pytest
 	ln -sfr .venv/$@ $@
 
 bin/restview: setup.py | bin/pip

setup.py

@@ -61,9 +61,8 @@ def get_version(filename='src/restview/restviewhttp.py'):
     package_data={'restview': ['*.css', '*.ico']},
     include_package_data=True,
     install_requires=['docutils', 'readme_renderer', 'pygments'],
-    extras_require={'syntax': [], 'test': ['mock']},
+    extras_require={'syntax': [], 'test': []},
     test_suite='restview.tests.test_suite',
-    tests_require=['mock'],
     zip_safe=False,
     entry_points="""
     [console_scripts]

src/restview/tests.py

@@ -5,9 +5,9 @@
 import unittest
 import webbrowser
 from io import StringIO
+from unittest.mock import Mock, patch
 
 import docutils.utils
-from mock import Mock, patch
 
 from restview.restviewhttp import (
     MyRequestHandler,