Change to readonly git protocol for podd so that ujsers without an

ssh key installed on github can still get podd.  (No one should be uploading
changes to podd).

.gitmodules

 [submodule "podd"]
 	path = podd
-	url = git@github.com:sawjlab/podd.git
+	url = git://github.com/sawjlab/podd.git