Make Plugin class sortable

Typically, it is expected that `LintRoller::Plugin#about` includes a name,
and sorting would be performed based on that name. However, currently,
executing `sort` on LintRoller results in the following error:

```console
ArgumentError: comparison of LintRoller::PluginTest::SampleRoller with LintRoller::PluginTest::AnotherRoller failed
```

This PR makes `LintRoller::Plugin` sortable by name. I considered including the version as well,
but I could not come up with any use cases where multiple plugins with the same name would need to be processed simultaneously.

lib/lint_roller/plugin.rb

@@ -18,5 +18,9 @@ def supported?(context)
     def rules(context)
       raise Error.new("Please implement `rules(context)` and return an instance of LintRoller::Rules")
     end
+
+    def <=>(other)
+      about.name <=> other.about.name
+    end
   end
 end

test/lib/plugin_test.rb

@@ -45,6 +45,35 @@ def rules(context)
       end
     end
 
+    class AnotherRoller < Plugin
+      ABOUT = About.new(
+        name: "another-roller",
+        version: "1.2.3",
+        homepage: "https://example.com",
+        description: "A sample lint roller for sort testing"
+      ).freeze
+
+      def about
+        ABOUT
+      end
+
+      def supported?(context)
+        [:standard, :rubocop].include?(context.runner)
+      end
+
+      def rules(context)
+        if @config[:💥] == true
+          Rules.new(error: Error.new("Unexpected Boom"))
+        else
+          Rules.new(
+            type: :path,
+            config_format: :rubocop,
+            value: "/some/path/to/a/place"
+          )
+        end
+      end
+    end
+
     def test_sample_roller
       sample_roller = SampleRoller.new(:some_config)
 
@@ -67,5 +96,12 @@ def test_sample_roller
         error: Error.new("Unexpected Boom")
       ), SampleRoller.new({:💥 => true}).rules(Context.new)
     end
+
+    def test_sort_sample_roller_with_another_roller
+      sample_roller = SampleRoller.new(:some_config)
+      another_roller = AnotherRoller.new(:some_config)
+
+      assert_equal [another_roller, sample_roller], [sample_roller, another_roller].sort
+    end
   end
 end