Fix CNAME

Dockerfile

@@ -22,7 +22,6 @@ RUN pip3 install --no-cache-dir --no-binary :all: \
         sphinx \
         breathe
 
-VOLUME /data/esphomedocs
 EXPOSE 8000
 WORKDIR /data/esphomedocs
 

conf.py

@@ -217,3 +217,4 @@ texinfo_documents = [
      'Miscellaneous'),
 ]
 linkcheck_ignore = [r'https://github.com/.*', r'https://discord.gg/.*']
+cname = os.getenv('CNAME', 'esphomelib.com')

githubpages.py

@@ -7,8 +7,9 @@ def create_nojekyll(app, env):
 
         path = os.path.join(app.builder.outdir, 'CNAME')
         with open(path, 'wt') as f:
-            f.write(os.getenv('CNAME', 'esphomelib.com'))
+            f.write(app.env.config.cname)
 
 
 def setup(app):
+    app.add_config_value('cname', 'esphomelib.com', 'html')
     app.connect('env-updated', create_nojekyll)