fix links for IPython example notebooks
fix links for IPython example notebooks

Jay-Oh-eN/nbviewer,twosigma/beaker-sharing-server,franblas/beaker-sharing-server,Jay-Oh-eN/nbviewer,christophelec/nbviewer,franblas/beaker-sharing-server,christophelec/nbviewer,AlfiyaZi/nbviewer,iamjakob/nbviewer,bollwyvl/nbviewer,thomasyu888/nbviewer,roxyboy/nbviewer,twosigma/beaker-sharing-server,AlfiyaZi/nbviewer,thomasyu888/nbviewer,twosigma/beaker-sharing-server,bollwyvl/nbviewer,franblas/beaker-sharing-server,roxyboy/nbviewer,Sage-Bionetworks/nbviewer,twosigma/beaker-sharing-server,Sage-Bionetworks/nbviewer,imsparsh/nbviewer,iamjakob/nbviewer,franblas/beaker-sharing-server,imsparsh/nbviewer