Replace failing spec with passing one in smoke test

The generated spec file intentionally has a failing spec in it, so gem
authors write specs.
If we are to use running specs as a way to check if the generator works,
then we need to make that spec pass.

smoke/smoke.rb

@@ -22,6 +22,12 @@
 
   gemspec_path.write gemspec
 
+  spec_path = gem_dir / "spec/rubocop/#{gem_name.split('-').last}_spec.rb"
+  spec = spec_path.read
+  spec.sub!('expect(false).to eq(true)', 'expect(true).to eq(true)')
+
+  spec_path.write spec
+
   system('bundle', 'install', exception: true, chdir: gem_dir)
   system('bundle', 'exec', 'rake', 'new_cop[Smoke/Foo]', exception: true, chdir: gem_dir)
   system('bundle', 'exec', 'rake', 'spec', exception: true, chdir: gem_dir)