fix broken import

add black dep for formatting

Author: platinummonkey

requirements.pip

@@ -1,3 +1,4 @@
+black==19.10b0
 coverage==5.0.3
 detox==0.19
 docutils==0.16

setup.py

@@ -8,6 +8,7 @@
 version = open('wiremock/VERSION', 'r').readline().strip()
 develop_requires = [
     'Sphinx~=2.4.3',
+    'black~=19.10b0',
     'coverage~=5.0.3',
     'detox~=0.19',
     'mock~=4.0.1',

wiremock/constants.py

@@ -3,6 +3,7 @@
 import logging
 
 from wiremock import __version__
+from wiremock._compat import add_metaclass
 
 
 logger = logging.getLogger('wiremock')