Update pyephem.sh

dhcpcd.service requires network.target.  

both are required before ipython can bind(?) to --ip=0.0.0.0

Doing adding such will wait/start iPython properly upon startup

```bash

[root@ephembox ~]# systemctl status ipython.service
ipython.service - iPython Notebook
	  Loaded: loaded (/usr/lib/systemd/system/ipython.service; enabled)
	  Active: active (running) since Tue, 2013-01-01 13:16:23 EST; 44s ago
	Main PID: 300 (ipython)
	  CGroup: name=systemd:/system/ipython.service
		  |-300 /bin/bash /home/john/ipython
		  `-305 /home/john/main/bin/python2 /home/john/main/bin/ipython notebook --ip=0.0.0.0

Jan 01 13:16:23 ephembox systemd[1]: Started iPython Notebook.
Jan 01 13:16:24 ephembox ipython[300]: [NotebookApp] Using existing profile dir: u'/root/.ipython/profile_default'
Jan 01 13:16:24 ephembox ipython[300]: [NotebookApp] Serving notebooks from /
Jan 01 13:16:24 ephembox ipython[300]: [NotebookApp] The IPython Notebook is running at: http://0.0.0.0:8888/
Jan 01 13:16:24 ephembox ipython[300]: [NotebookApp] Use Control-C to stop this server and shut down all kernels.
Jan 01 13:16:24 ephembox ipython[300]: [NotebookApp] No web browser found: could not locate runnable browser.