Fix small typo in magic.py.

Thanks @juliantaylor for pointing this out. Closes gh-425.

IPython/core/magic.py

@@ -3279,7 +3279,7 b' Defaulting color scheme to \'NoColor\'"""'
 
         This magic replaces IPython's threaded shells that were activated
         using the (pylab/wthread/etc.) command line flags.  GUI toolkits
-        can now be enabled, disabled and swtiched at runtime and keyboard
+        can now be enabled, disabled and changed at runtime and keyboard
         interrupts should work without any problems.  The following toolkits
         are supported:  wxPython, PyQt4, PyGTK, and Tk::