Update GLM_linear.ipynb (#6519)

* update link to john kruschkes book
* google plus has been stopped in 2018 - remove dead link

Author: bsenst

docs/source/learn/core_notebooks/GLM_linear.ipynb

@@ -391,9 +391,8 @@
    "source": [
     "For additional background, here are a few good resources on Bayesian statistics:\n",
     "\n",
-    "  - The excellent book [Doing Bayesian Data Analysis by John Kruschke](http://www.indiana.edu/~kruschke/DoingBayesianDataAnalysis/).\n",
+    "  - The excellent book [Doing Bayesian Data Analysis by John Kruschke](https://sites.google.com/site/doingbayesiandataanalysis).\n",
     "  - [Andrew Gelman's blog](http://andrewgelman.com/)\n",
-    "  - [Baeu Cronins blog post on Probabilistic Programming](https://plus.google.com/u/0/107971134877020469960/posts/KpeRdJKR6Z1)\n",
     "  \n",
     "Author: Thomas Wiecki"
    ]