Tidy up --exclude options in .yardopts (#960)

* Remove .yardopts exclude for removed file patch.rb

Seems like this file is no longer, deleted in c1ff325.

* Update .yardopts exclude path for plugin.rb

Set path to new location of patch.rb file updated in 308e3ca.

.yardopts

@@ -7,8 +7,7 @@
 --title            "Haml Documentation"
 --query            'object.type != :classvariable'
 --query            'object.type != :constant || @api && @api.text == "public"'
---exclude          lib/haml/template/patch.rb
---exclude          lib/haml/template/plugin.rb
+--exclude          lib/haml/plugin.rb
 --exclude          lib/haml/railtie.rb
 --exclude          lib/haml/helpers/action_view_mods.rb
 --exclude          lib/haml/helpers/xss_mods.rb