Fix doc formating

Fix formating issue in the doc/source/plugin.rst

Trivial fix.

Change-Id: Ifc9a43aebdab0c15c83485cf0b6d4133d7194a9d
diff --git a/doc/source/plugins.rst b/doc/source/plugins.rst
index 31987bc..5b3c6cf 100644
--- a/doc/source/plugins.rst
+++ b/doc/source/plugins.rst
@@ -99,7 +99,7 @@
       should exist at this point.
    -  **extra** - Called near the end after layer 1 and 2 services have
       been started.
-   - **test-config** - Called at the end of devstack used to configure tempest
+   -  **test-config** - Called at the end of devstack used to configure tempest
       or any other test environments
 
 -  **unstack** - Called by ``unstack.sh`` before other services are shut