[docs] fix some changelog links
[docs] fix some changelog links

jcb91/IPython-notebook-extensions,jcb91/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,jcb91/IPython-notebook-extensions