plugin.rst: Fix a typo in an example code fragment

Change-Id: Ib003702533397a2f0f3efc68f75662cad2208301
diff --git a/doc/source/plugin.rst b/doc/source/plugin.rst
index f92f63e..72db6e9 100644
--- a/doc/source/plugin.rst
+++ b/doc/source/plugin.rst
@@ -29,9 +29,9 @@
 abstract class that should be used as the parent for your plugin. To use this
 you would do something like the following::
 
-  from tempest.test_discover import plugin
+  from tempest.test_discover import plugins
 
-  class MyPlugin(plugin.TempestPlugin):
+  class MyPlugin(plugins.TempestPlugin):
 
 Then you need to ensure you locally define all of the methods in the abstract
 class, you can refer to the api doc below for a reference of what that entails.