coverage: Don't require coverage in six.PY2/PY3 branches.

tools/coveragerc

@@ -7,6 +7,9 @@ exclude_lines =
     if False:
     # Don't require coverage for base class NotImplementedErrors
     raise NotImplementedError()
+    # Don't require coverage for Python 2/3 variations; it's impossible to cover on both
+    if six.PY3:
+    if six.PY2:
 
 [run]
 omit =

zerver/lib/bugdown/__init__.py

@@ -67,7 +67,7 @@ def unescape(s):
     # type: (Text) -> (Text)
     if six.PY2:
         return html_parser.HTMLParser().unescape(s)
-    else:
+    elif six.PY3:
         return html.unescape(s)
 
 def list_of_tlds():