Fix tokenization of compact class names in Ruby lexer (rouge-ruby#1470)

The Ruby lexer currently tokenises compact class names differently to
how they are tokenised if nested. This commit makes both results
consistent.

lib/rouge/lexers/ruby.rb

@@ -309,6 +309,8 @@ def self.detect?(text)
 
       state :classname do
         rule %r/\s+/, Text
+        rule %r/\w+(::\w+)+/, Name::Class
+
         rule %r/\(/ do
           token Punctuation
           push :defexpr

spec/visual/samples/ruby

@@ -78,6 +78,45 @@ class Ipsum < Lorem
   end
 end
 
+########
+# Various types of class definitions
+########
+
+# Singleton class definition
+module Table
+  module Row
+    DEFAULTS = { cell_width: 80, cell_height: 60 }
+
+    class << self
+      def styles hsh
+        hsh.merge DEFAULTS
+      end
+    end
+  end
+end
+
+# Nested class name
+module Table
+  module Row
+    class Cell < Table::Block
+      WIDTH = TABLE::ROW::styles[:cell_width]
+
+      def text string, width = WIDTH
+        string.center width
+      end
+    end
+  end
+end
+
+# Compact class name
+class Table::Row::Cell < Table::Block
+  WIDTH = TABLE::ROW::styles[:cell_width]
+
+  def text string, width = WIDTH
+    string.center width
+  end
+end
+
 ########
 # The popular . :bow:
 ########