move pachyderm PFS link above rex ray link in docs/extend/plugins.md

Signed-off-by: Peter Edge <peter.edge@gmail.com>

docs/extend/plugins.md

@@ -55,14 +55,14 @@ The following plugins exist:
   a plugin that provides credentials and secret management using Keywhiz as
   a central repository.
 
-* The [REX-Ray plugin](https://github.com/emccode/rexraycli) is a volume plugin
-  which is written in Go and provides advanced storage functionality for many
-  platforms including EC2, OpenStack, XtremIO, and ScaleIO.
-
 * The [Pachyderm PFS plugin](https://github.com/pachyderm/pachyderm/tree/master/src/cmd/pfs-volume-driver)
   is a volume plugin written in Go that provides functionality to mount Pachyderm File System (PFS)
   repositories at specific commits as volumes within Docker containers.
 
+* The [REX-Ray plugin](https://github.com/emccode/rexraycli) is a volume plugin
+  which is written in Go and provides advanced storage functionality for many
+  platforms including EC2, OpenStack, XtremIO, and ScaleIO.
+
 ## Troubleshooting a plugin
 
 If you are having problems with Docker after loading a plugin, ask the authors