Merge "Fix html_last_updated_fmt for Python3"

doc/source/conf.py

@@ -128,8 +128,11 @@ html_theme = 'nature'
 # using the given strftime format.
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
            "-n1"]
-html_last_updated_fmt = subprocess.Popen(
-    git_cmd, stdout=subprocess.PIPE).communicate()[0]
+try:
+    html_last_updated_fmt = subprocess.check_output(git_cmd).decode('utf-8')
+except Exception:
+    warnings.warn('Cannot get last updated time from git repository. '
+                  'Not setting "html_last_updated_fmt".')
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.