message: gen_doc: strip trailing space
  Lots of editors do this by default. It is cleaner.
diff: @@ -105,7 +105,7 @@ def display_schema(schema: OpSchema, versions: Sequence[OpSchema]) -> Text:
  # doc
  if schema.doc:
  s += '\n'
  - s += '\n'.join(' ' + line
  + s += '\n'.join((' ' + line).rstrip()
  for line in schema.doc.lstrip().splitlines())
  s += '\n'
  