core: _actually_ fix caveats

there was another untested place where the cask methods were being
re-implemented. these were preventing casks with caveats from working
properly.

refs Homebrew#9494

lib/hbc/caveats.rb

@@ -29,11 +29,11 @@ def version
   end
 
   def caskroom_path
-    @cask.class.caskroom.join(token)
+    @cask.caskroom_path
   end
 
   def staged_path
-    caskroom_path.join(@cask.version.to_s)
+    @cask.staged_path
   end
 
   # DSL. Each method should handle output, following the convention of