Pin voluptuous version

Closes https://github.com/esphome/esphome/pull/745

setup.py

@@ -23,7 +23,7 @@ GITHUB_URL = 'https://github.com/{}'.format(GITHUB_PATH)
 DOWNLOAD_URL = '{}/archive/v{}.zip'.format(GITHUB_URL, const.__version__)
 
 REQUIRES = [
-    'voluptuous>=0.11.5,<0.12',
+    'voluptuous==0.11.5',
     'PyYAML>=5.1,<6',
     'paho-mqtt>=1.4,<2',
     'colorlog>=4.0.2',