Use svg by default due to lack of Ghostscript by default on Windows

IPython/extensions/octavemagic.py

@@ -73,7 +73,7 b' class OctaveMagics(Magics):'
         """
         super(OctaveMagics, self).__init__(shell)
         self._oct = oct2py.Oct2Py()
-        self._plot_format = 'png'
+        self._plot_format = 'svg'
 
         # Allow publish_display_data to be overridden for
         # testing purposes.