remove tagged version for ipython optioanl requirement

- ipython is now in the 5.x series
- the old ipython[all] conflicts with juoyter

Author: etpinard

optional-requirements.txt

@@ -15,8 +15,8 @@ numpy
 nose==1.3.3
 coverage
 
-## ipython dependencies ##
-ipython[all]==3.0.0
+## ipython ##
+ipython
 
 ## pandas deps for some matplotlib functionality ##
 pandas