Enable Gemspec/DeprecatedAttributeAssignment rule
What does this MR do and why?
This MR enables Gemspec/DeprecatedAttributeAssignment
to discourage the use of deprecated attributes to make packages smaller by, for example, stop shipping test_files
. See https://github.com/rubygems/guides/issues/90.
Contributes to #40.
Edited by Peter Leitzen