Use relative URL for TIMPI submodule.
Use relative URL for TIMPI submodule.

Technically we could use a single ../ but I think this helps make it
more clear that the TIMPI repo is located under the libMesh project.

If you already pulled a version with the previous URL, you may need to
run the command:

git submodule sync contrib/timpi

in order for the update URL to take effect.

Refs #2386.

libMesh/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,libMesh/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,libMesh/libmesh,libMesh/libmesh,dschwen/libmesh,jwpeterson/libmesh,roystgnr/libmesh,capitalaslash/libmesh,dschwen/libmesh,libMesh/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,dschwen/libmesh,roystgnr/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,dschwen/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,roystgnr/libmesh,libMesh/libmesh,libMesh/libmesh,libMesh/libmesh,dschwen/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,dschwen/libmesh,dschwen/libmesh,jwpeterson/libmesh,roystgnr/libmesh,capitalaslash/libmesh,dschwen/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh