[ci] allow lint failure on travis isort changes its mind so often that this lint build is becoming more of a nuisance than helpful
[ci] allow lint failure on travis
isort changes its mind so often that this lint build is becoming more of a
nuisance than helpful

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