rubocop: rearranged the config after review

Style/HashSyntax: do enforce it, for new code
Style/MultilineOperationIndentation: indented is right
Style/VariableName: Style/MethodName: do not spell out snake_case
  which is the default
better type info in doc comments
Fixed a condition that was always true.

The impact of the bug was small because other code queried DNS anyway and
filtered out the nonexistent host name.